scispace - formally typeset
Search or ask a question

Showing papers by "Fabian Walter published in 2008"


Journal ArticleDOI
TL;DR: In this paper, the star formation efficiency (SFE) per unit of gas in 23 nearby galaxies and compare it with expectations from proposed star formation laws and thresholds was measured, and the authors interpreted this decline as a strong dependence of giant molecular cloud (GMC) formation on environment.
Abstract: We measure the star formation efficiency (SFE), the star formation rate (SFR) per unit of gas, in 23 nearby galaxies and compare it with expectations from proposed star formation laws and thresholds. We use H I maps from The H I Nearby Galaxy Survey (THINGS) and derive H2 maps of CO measured by HERA CO-Line Extragalactic Survey and Berkeley-Illinois-Maryland Association Survey of Nearby Galaxies. We estimate the SFR by combining Galaxy Evolution Explorer (GALEX) far-ultraviolet maps and the Spitzer Infrared Nearby Galaxies Survey (SINGS) 24 ?m maps, infer stellar surface density profiles from SINGS 3.6 ?m data, and use kinematics from THINGS. We measure the SFE as a function of the free fall and orbital timescales, midplane gas pressure, stability of the gas disk to collapse (including the effects of stars), the ability of perturbations to grow despite shear, and the ability of a cold phase to form. In spirals, the SFE of H2 alone is nearly constant at (5.25 ? 2.5) ? 10?10 yr?1 (equivalent to an H2 depletion time of 1.9 ? 109 yr) as a function of all of these variables at our 800 pc resolution. Where the interstellar medium (ISM) is mostly H I, however, the SFE decreases with increasing radius in both spiral and dwarf galaxies, a decline reasonably described by an exponential with scale length 0.2r 25-0.25r 25. We interpret this decline as a strong dependence of giant molecular cloud (GMC) formation on environment. The ratio of molecular-to-atomic gas appears to be a smooth function of radius, stellar surface density, and pressure spanning from the H2-dominated to H I-dominated ISM. The radial decline in SFE is too steep to be reproduced only by increases in the free-fall time or orbital time. Thresholds for large-scale instability suggest that our disks are stable or marginally stable and do not show a clear link to the declining SFE. We suggest that ISM physics below the scales that we observe?phase balance in the H I, H2 formation and destruction, and stellar feedback?governs the formation of GMCs from H I.

1,888 citations


Journal ArticleDOI
TL;DR: In this article, the authors present a comprehensive analysis of the relationship between star formation rate surface density and gas surface density at sub-kpc resolution in a sample of 18 nearby galaxies and investigate how the star formation law differs between the H2 dominated centers of spiral galaxies, their H I dominated outskirts and the H I rich late-type/dwarf galaxies.
Abstract: We present a comprehensive analysis of the relationship between star formation rate surface density, ΣSFR, and gas surface density, Σgas, at sub-kpc resolution in a sample of 18 nearby galaxies. We use high-resolution H I data from The H I Nearby Galaxy Survey, CO data from HERACLES and the BIMA Survey of Nearby Galaxies, 24 μm data from the Spitzer Space Telescope, and UV data from the Galaxy Evolution Explorer. We target seven spiral galaxies and 11 late-type/dwarf galaxies and investigate how the star formation law differs between the H2 dominated centers of spiral galaxies, their H I dominated outskirts and the H I rich late-type/dwarf galaxies. We find that a Schmidt-type power law with index N = 1.0 ± 0.2 relates ΣSFR and ΣH2 across our sample of spiral galaxies, i.e., that H2 forms stars at a constant efficiency in spirals. The average molecular gas depletion time is ~2 × 109 years. The range of ΣH2 over which we measure this relation is ~3-50 M ☉ pc–2, significantly lower than in starburst environments. We find the same results when performing a pixel-by-pixel analysis, averaging in radial bins, or when varying the star formation tracer used. We interpret the linear relation and constant depletion time as evidence that stars are forming in giant molecular clouds with approximately uniform properties and that ΣH2 may be more a measure of the filling fraction of giant molecular clouds than changing conditions in the molecular gas. The relationship between total gas surface density (Σgas) and ΣSFR varies dramatically among and within spiral galaxies. Most galaxies show little or no correlation between ΣHI and ΣSFR. As a result, the star formation efficiency (SFE), ΣSFR/Σgas, varies strongly across our sample and within individual galaxies. We show that this variation is systematic and consistent with the SFE being set by local environmental factors: in spirals the SFE is a clear function of radius, while the dwarf galaxies in our sample display SFEs similar to those found in the outer optical disks of the spirals. We attribute the similarity to common environments (low density, low metallicity, H I dominated) and argue that shear (which is typically absent in dwarfs) cannot drive the SFE. In addition to a molecular Schmidt law, the other general feature of our sample is a sharp saturation of H I surface densities at ΣHI ≈ 9 M ☉ pc–2 in both the spiral and dwarf galaxies. In the case of the spirals, we observe gas in excess of this limit to be molecular.

1,842 citations


Journal ArticleDOI
TL;DR: The HI Nearby Galaxy Survey (THINGS) as discussed by the authors is a high spectral (≤52kms −1 ) and spatial (∼ 6 ′′ ) resolution survey of HI emission in 34 nearby galaxies obtained using the NRAO Very Large Array (VLA).
Abstract: We present “The HI Nearby Galaxy Survey (THINGS)”, a high spectral (≤52kms −1 ) and spatial (∼ 6 ′′ ) resolution survey of HI emission in 34 nearby galaxies obtained using the NRAO Very Large Array (VLA) The overarching scientific goal of THINGS is to investigate fundamental characteristics of the interstellar medium (ISM) related to galaxy morphology, star formation and mass distribution across the Hubble sequence Unique characteristics of the THINGS database are the homogeneous sensitivity as well as spatial and velocity resolution of the HI data which is at the limit of what can be achieved with the VLA for a significant number of galaxies A sample of 34 objects at distances 2 < D <15 Mpc (resulting in linear resolutions of ∼100 to 500pc) are targeted in THINGS, covering a wide range of star formation rates (∼ 10 −3 to 6 M⊙ yr −1 ), total HI masses MHI (001 to 14×10 9 M⊙), absolute luminosities MB (–115 to –217mag) and metallicities (75 to 92 in units of 12+log[O/H]) We describe the setup of the VLA observations, the data reduction procedures and the creation of the final THINGS data products We present an atlas of the integrated HI maps, the velocity fields, the second moment (velocity dispersion) maps and individual channel maps of each THINGS galaxy The THINGS data products are made publicly available through a dedicated webpage Accompanying THINGS papers address issues such as the small–scale structure of the ISM, the (dark) matter distribution in THINGS galaxies, and the processes leading to star formation Subject headings: surveys — galaxies: structure — galaxies: ISM — ISM: general — ISM: atoms — radio lines: galaxies

1,354 citations


Journal ArticleDOI
TL;DR: In this article, rotation curves of 19 galaxies from the H I Nearby Galaxy Survey (THINGS) were used to derive the geometric and dynamical parameters using H I data alone and the rotation curves were combined with 3.6 μm data from the Spitzer Infrared Nearby Galaxies Survey to construct mass models.
Abstract: We present rotation curves of 19 galaxies from The H I Nearby Galaxy Survey (THINGS). The high spatial and velocity resolution of THINGS make these the highest quality H I rotation curves available to date for a large sample of nearby galaxies, spanning a wide range of H I masses and luminosities. The high quality of the data allows us to derive the geometric and dynamical parameters using H I data alone. We do not find any declining rotation curves unambiguously associated with a cut-off in the mass distribution out to the last measured point. The rotation curves are combined with 3.6 μm data from the Spitzer Infrared Nearby Galaxies Survey to construct mass models. Our best-fit dynamical disk masses, derived from the rotation curves, are in good agreement with photometric disk masses derived from the 3.6 μm images in combination with stellar population synthesis arguments and two different assumptions for the stellar initial mass function (IMF). We test the cold dark matter (CDM) motivated cusp model, and the observationally motivated central density core model and find that (independent of IMF) for massive, disk-dominated galaxies, all halo models fit apparently equally well; for low-mass galaxies, however, a core-dominated halo is clearly preferred over a cusp-like halo. The empirically derived densities of the dark matter halos of the late-type galaxies in our sample are half of what is predicted by CDM simulations, again independent of the assumed IMF.

948 citations


Journal ArticleDOI
TL;DR: In this article, high-resolution observations of CO were used to systematically measure the resolved size-line width, luminosity line width, and luminosity-size, and mass-luminosity relations of GMCs in a variety of extragalactic systems.
Abstract: We use high spatial resolution observations of CO to systematically measure the resolved size-line width, luminosity-line width, luminosity-size, and mass-luminosity relations of GMCs in a variety of extragalactic systems. Although the data are heterogeneous, we analyze them in a consistent manner to remove the biases introduced by limited sensitivity and resolution, thus obtaining reliable sizes, velocity dispersions, and luminosities. We compare the results obtained in dwarf galaxies with those from the Local Group spiral galaxies. We find that extragalactic GMC properties measured across a wide range of environments are very much compatible with those in the Galaxy. The property that shows the largest variability is their resolved brightness temperature, although even that is similar to the average Galactic value in most sources. We use these results to investigate metallicity trends in the cloud average column density and virial CO-to-H2 factor. We find that these measurements do not accord with simple predictions from photoionization-regulated star formation theory, although this could be due to the fact that we do not sample small enough spatial scales or the full gravitational potential of the molecular cloud. We also find that the virial CO-to-H2 conversion factor in CO-bright GMCs is very similar to Galactic and that the excursions do not show a measurable metallicity trend. We contrast these results with estimates of molecular mass based on far-infrared measurements obtained for the Small Magellanic Cloud, which systematically yield larger masses, and interpret this discrepancy as arising from large H2 envelopes that surround the CO-bright cores. We conclude that GMCs identified on the basis of their CO emission are a unique class of objects that exhibit a remarkably uniform set of properties from galaxy to galaxy.

576 citations


Journal ArticleDOI
TL;DR: In this paper, a new method was proposed to remove the impact of random and small-scale noncircular motions from H I velocity fields in (dwarf) galaxies in order to better constrain the dark matter properties for these objects.
Abstract: We present a new method to remove the impact of random and small-scale noncircular motions from H I velocity fields in (dwarf) galaxies in order to better constrain the dark matter properties for these objects. This method extracts the circularly rotating velocity components from the H I data cube and condenses them into a so-called bulk velocity field. We derive high-resolution (~0.2 kpc) rotation curves of IC 2574 and NGC 2366 based on bulk velocity fields derived from The H I Nearby Galaxy Survey obtained at the Very Large Array. We compare the bulk velocity field rotation curves with those derived from the traditional intensity-weighted mean velocity fields and find significant differences. The bulk velocity field rotation curves are significantly less affected by noncircular motions and constrain the dark matter distribution in our galaxies, allowing us to address the discrepancy between the inferred and predicted dark matter distribution in galaxies (the "cusp/core" problem). Spitzer Infrared Nearby Galaxies Survey 3.6 μm data, which are largely unaffected by dust in these systems, as well as ancillary optical information, are used to separate the contribution of the baryons from the total matter content. Using stellar population synthesis models, assuming various sets of metallicity and star-formation histories, we compute stellar mass-to-light ratios for the 3.6 μm and 4.5 μm bands. Using our predicted value for the 3.6 μm stellar mass-to-light ratio, we find that the observed dark matter distributions of IC 2574 and NGC 2366 are inconsistent with the cusp-like dark matter halo predicted by Λ Cold Dark Matter models, even after corrections for noncircular motions. This result also holds for other assumptions about the stellar mass-to-light ratio. The distribution of dark matter within our sample galaxies is best described by models with a kpc-sized constant-density core.

316 citations


Journal ArticleDOI
TL;DR: In this article, a method to remove the impact of random and small-scale non-circular motions from HI velocity fields in galaxies in order to better constrain the dark matter properties for these objects is presented.
Abstract: We present a new method to remove the impact of random and small-scale non-circular motions from HI velocity fields in galaxies in order to better constrain the dark matter properties for these objects. This method extracts the circularly rotating velocity components from the HI data cube and condenses them into a so-called bulk velocity field. We derive high-resolution rotation curves of IC 2574 and NGC 2366 based on bulk velocity fields derived from The HI Nearby Galaxy Survey (THINGS) obtained at the VLA. The bulk velocity field rotation curves are significantly less affected by non-circular motions and constrain the dark matter distribution in our galaxies, allowing us to address the discrepancy between the inferred and predicted dark matter distribution in galaxies (the "cusp/core" problem). Spitzer Infrared Nearby Galaxies Survey (SINGS) 3.6 micron data as well as ancillary optical information, are used to separate the baryons from the total matter content. Using stellar population synthesis models, assuming various sets of metallicity and star formation histories, we compute stellar mass-to-light ratios for the 3.6 and 4.5 micron bands. Using our predicted value for the 3.6 micron stellar mass-to-light ratio, we find that the observed dark matter distributions of IC 2574 and NGC 2366 are inconsistent with the cuspy dark matter halo predicted by LCDM models, even after corrections for non-circular motions. This result also holds for other assumptions about the stellar mass-to-light ratio. The distribution of dark matter within our sample galaxies is best described by models with a kpc-sized constant-density core.

290 citations


Journal ArticleDOI
TL;DR: In this article, the authors measured the star formation efficiency (SFE) in 23 nearby galaxies and compared it to expectations from proposed star formation laws and thresholds. And they found that the SFE of H2 alone is nearly constant at 5.25 +/- 2.25 r_25.
Abstract: We measure the star formation efficiency (SFE), the star formation rate per unit gas, in 23 nearby galaxies and compare it to expectations from proposed star formation laws and thresholds. We use HI maps from THINGS and derive H2 maps from HERACLES and BIMA SONG CO. We estimate the star formation rate by combining GALEX FUV maps and SINGS 24 micron maps, infer stellar surface density profiles from SINGS 3.6 micron data, and use kinematics from THINGS. We measure the SFE as a function of: the free-fall and orbital timescales; midplane gas pressure; stability of the gas disk to collapse (including the effects of stars); the ability of perturbations to grow despite shear; and the ability of a cold phase to form. In spirals, the SFE of H2 alone is nearly constant at 5.25 +/- 2.5 x 10^(-10) yr^(-1) (equivalent to an H2 depletion time of 1.9x10^9 yr) as a function of all of these variables at our 800 pc resolution. Where the ISM is mostly HI, on the other hand, the SFE decreases with increasing radius in both spiral and dwarf galaxies, a decline reasonably described by an exponential with scale length 0.2-0.25 r_25. We interpret this decline as a strong dependence of GMC formation on environment. The ratio of H2 to HI appears to be a smooth function of radius, stellar surface density, and pressure spanning from the H2-dominated to HI-dominated ISM. The radial decline in SFE is too steep to be reproduced only by increases in the free-fall time or orbital time. Thresholds for large-scale instability suggest that our disks are stable or marginally stable and do not show a clear link to the declining SFE. We suggest that ISM physics below the scales that we observe - phase balance in the HI, H2 formation and destruction, and stellar feedback - governs the formation of GMCs from HI.

181 citations


Journal ArticleDOI
TL;DR: In this article, the authors present a study of the rest-frame far-infrared (FIR) properties of the sample of the 33 quasars known with the Max Planck Millimeter Bolometer Array (MAMBO) at 250 GHz with mJy sensitivity, and 30% of them were detected.
Abstract: We report new continuum observations of 14 -->z ~ 6 quasars at 250 GHz and 14 quasars at 1.4 GHz. We summarize all recent millimeter and radio observations of the sample of the 33 quasars known with -->5.71 ? z? 6.43 and present a study of the rest-frame far-infrared (FIR) properties of this sample. These quasars were observed with the Max Planck Millimeter Bolometer Array (MAMBO) at 250 GHz with mJy sensitivity, and 30% of them were detected. We also recover the average 250 GHz flux density of the MAMBO undetected sources at 4 ? by stacking the on-source measurements. The derived mean radio-to-UV spectral energy distributions (SEDs) of the full sample and the 250 GHz nondetections show no significant differences from lower redshift optical quasars. Obvious FIR excesses are seen in the individual SEDs of the strong 250 GHz detections, with FIR-to-radio emission ratios consistent with those of typical star-forming galaxies. Most 250 GHz-detected sources follow the LFIR-Lbol relationship derived from a sample of local IR-luminous quasars ( -->LIR > 1012 L?), while the average LFIR/Lbol ratio of the nondetections is consistent with that of the optically selected PG quasars. The MAMBO detections also tend to have weaker Ly? emission than the nondetected sources. We discuss possible FIR dust-heating sources and critically assess the possibility of active star formation in the host galaxies of the -->z ~ 6 quasars. The average star formation rate of the MAMBO nondetections is likely to be less than a few hundred M? yr?1, but in the strong detections, the host galaxy star formation is probably at a rate of 103 M? yr?1, which dominates the FIR dust heating.

169 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present harmonic decompositions of the velocity fields of 19 galaxies from the H I Nearby Galaxy Survey (THINGS) which quantify the magnitude of the noncircular motions in these galaxies and yield observational estimates of the elongations of the dark matter halo potentials.
Abstract: We present harmonic decompositions of the velocity fields of 19 galaxies from The H I Nearby Galaxy Survey (THINGS) which quantify the magnitude of the noncircular motions in these galaxies and yield observational estimates of the elongations of the dark matter halo potentials. Additionally, we present accurate dynamical center positions for these galaxies. We show that the positions of the kinematic and photometric centers of the large majority of the galaxies in our sample are in good agreement. The median absolute amplitude of the noncircular motions, averaged over our sample, is 6.7 km s?1, with ~90% of the galaxies having median noncircular motions of less than ~9 km s?1. As a fraction of the total rotation velocity, this translates into 4.5% on average. The mean elongation of the gravitational potential, after a statistical correction for an unknown viewing angle, is 0.017 ? 0.020, which is consistent with a round potential. Our derived noncircular motions and elongations are smaller than what is needed to bring cold dark matter (CDM) simulations in agreement with the observations. In particular, the amplitudes of the noncircular motions are not high enough to hide the steep central mass-density profiles predicted by CDM simulations. We show that the amplitudes of the noncircular motions decrease toward lower luminosities and later Hubble types.

162 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present observations and analysis of nine dwarf irregular galaxies (dIs) in the M81 Group taken with the Advanced Camera for Surveys aboard the Hubble Space Telescope, and analyze the similarities and differences in the star formation histories (SFHs), birthrate parameters, fraction of stars formed per time interval (f), and spatial distribution of stellar components.
Abstract: We present observations and analysis of nine dwarf irregular galaxies (dIs) in the M81 Group taken with the Advanced Camera for Surveys aboard the Hubble Space Telescope. The nine galaxies (the Garland, M81 Dwarf A, DDO 53, Ho IX, Ho I, DDO 165, NGC 2366, Ho II, and IC 2574) span 6 mag in luminosity, a factor of 1000 in current star formation rate, and 0.5 dex in metallicity. We use color-magnitude diagrams of resolved stellar populations to study the star formation histories (SFHs) of these galaxies. Dividing the sample at MB = − 15, we analyze the similarities and differences in the SFHs, birthrate parameters (b), fraction of stars formed per time interval (f), and spatial distribution of stellar components. As function of luminosity, we find only minor differences in SF characteristics among the M81 Group dIs despite a wide range of physical properties. We extend our comparison to select dIs in the Local Group (LG) and, again, find little variation in SF parameters. Our average f parameters are consistent with a constant SFH; however, individual galaxies can show significant departures from this. We find this result underlines the importance of stochastic SF in dIs. We also compare possible formation scenarios of the fainter and candidate tidal dwarfs (TDGs) in the M81 Group. The SFHs and the spatial distribution of associated red stars suggest that the Garland and Ho IX are not dIs and are potentially TDGs. A noteworthy difference between the LG and the M81 Group is the lack of TDGs in the LG.

Journal ArticleDOI
TL;DR: In this article, the authors present harmonic decompositions of the velocity fields of 19 galaxies from THINGS (The HI Nearby Galaxy Survey) which quantify the magnitude of the non-circular motions in these galaxies and yield observational estimates of the elongations of the dark matter halo potentials.
Abstract: We present harmonic decompositions of the velocity fields of 19 galaxies from THINGS (The \HI Nearby Galaxy Survey) which quantify the magnitude of the non-circular motions in these galaxies and yield observational estimates of the elongations of the dark matter halo potentials. Additionally, we present accurate dynamical center positions for these galaxies. We show that the positions of the kinematic and photometric centers of the large majority of the galaxies in our sample are in good agreement. The median absolute amplitude of the non-circular motions, averaged over our sample, is $6.7 \kms$, with $\sim 90$ percent of the galaxies having median non-circular motions of less than $\sim 9\kms$. As a fraction of the total rotation velocity this translates into 4.5 percent on average. The mean elongation of the gravitational potential, after a statistical correction for an unknown viewing angle, is $0.017\pm 0.020$, i.e., consistent with a round potential. Our derived non-circular motions and elongations are smaller than what is needed to bring Cold Dark Matter (CDM) simulations in agreement with the observations. In particular, the amplitudes of the non-circular motions are not high enough to hide the steep central mass-density profiles predicted by CDM simulations. We show that the amplitudes of the non-circular motions decrease towards lower luminosities and later Hubble types.

Journal ArticleDOI
TL;DR: In this article, the authors present a comprehensive analysis of the relationship between star formation rate surface density and gas surface density at sub-kpc resolution in a sample of 18 nearby galaxies using high resolution HI data from THINGS, CO data from HERACLES and BIMA SONG, 24 micron data from the Spitzer Space Telescope and UV data from GALEX.
Abstract: (Abridged) We present a comprehensive analysis of the relationship between star formation rate surface density (SFR SD) and gas surface density (gas SD) at sub-kpc resolution in a sample of 18 nearby galaxies. We use high resolution HI data from THINGS, CO data from HERACLES and BIMA SONG, 24 micron data from the Spitzer Space Telescope, and UV data from GALEX. We target 7 spiral galaxies and 11 late-type/dwarf galaxies and investigate how the star formation law differs between the H2-dominated centers of spiral galaxies, their HI-dominated outskirts and the HI-rich late-type/dwarf galaxies. We find that a Schmidt-type power law with index N=1.0+-0.2 relates the SFR SD and the H2 SD across our sample of spiral galaxies, i.e., that H2 forms stars at a constant efficiency in spirals. The average molecular gas depletion time is ~2*10^9 yrs. We interpret the linear relation and constant depletion time as evidence that stars are forming in GMCs with approximately uniform properties and that the H2 SD may be more a measure of the filling fraction of giant molecular clouds than changing conditions in the molecular gas. The relationship between total gas SD and SFR SD varies dramatically among and within spiral galaxies. Most galaxies show little or no correlation between the HI SD and the SFR SD. As a result, the star formation efficiency (SFE = SFR SD / gas SD) varies strongly across our sample and within individual galaxies. We show that in spirals the SFE is a clear function of radius, while the dwarf galaxies in our sample display SFEs similar to those found in the outer optical disks of the spirals. Another general feature of our sample is a sharp saturation of the HI SD at ~9 M_sol/pc^2 in both the spiral and dwarf galaxies.

Journal ArticleDOI
TL;DR: The average star formation rate of the MAMBO non-detections is likely to be less than a few hundred M{\odot} yr^{-1}, but in the strong detections, the host galaxy star formation is probably at a rate of 10−3 M{ \gtrsim10−12} L{L_{\odots} yr−1, which dominates the FIR dust heating.
Abstract: We report new continuum observations of fourteen z~6 quasars at 250 GHz and fourteen quasars at 1.4 GHz. We summarize all recent millimeter and radio observations of the sample of the thirty-three quasars known with 5.71 10^{12}L_{\odot}), while the average L_{FIR}/L_{bol} ratio of the non-detections is consistent with that of the optically-selected PG quasars. The MAMBO detections also tend to have weaker Ly\alpha emission than the non-detected sources. We discuss possible FIR dust heating sources, and critically assess the possibility of active star formation in the host galaxies of the z~6 quasars. The average star formation rate of the MAMBO non-detections is likely to be less than a few hundred M_{\odot} yr^{-1}, but in the strong detections, the host galaxy star formation is probably at a rate of \gtrsim10^{3} M_{\odot} yr^{-1}, which dominates the FIR dust heating.

Journal ArticleDOI
TL;DR: In this paper, the average angular offset between the H I and 24 μm emissivity peaks as a function of radius was measured for a sample of 14 nearby disk galaxies, and the resulting values of t H I24 μm for the sample are in the range 1-4 Myr.
Abstract: We estimate a characteristic timescale for star formation in the spiral arms of disk galaxies, going from atomic hydrogen (H I) to dust-enshrouded massive stars. Drawing on high-resolution H I data from The H I Nearby Galaxy Survey and 24 μm images from the Spitzer Infrared Nearby Galaxies Survey, we measure the average angular offset between the H I and 24 μm emissivity peaks as a function of radius, for a sample of 14 nearby disk galaxies. We model these offsets assuming an instantaneous kinematic pattern speed, Ω p , and a timescale, t H I24 μm, for the characteristic time span between the dense H I phase and the formation of massive stars that heat the surrounding dust. Fitting for Ω p and t H I24 μm, we find that the radial dependence of the observed angular offset (of the H I and 24 μm emission) is consistent with this simple prescription; the resulting corotation radii of the spiral patterns are typically R cor 2.7Rs , consistent with independent estimates. The resulting values of t H I24 μm for the sample are in the range 1-4 Myr. We have explored the possible impact of non-circular gas motions on the estimate of t H I24 μm and have found it to be substantially less than a factor of 2. This implies a short timescale for the most intense phase of the ensuing star formation in spiral arms, and implies that a considerable fraction of molecular clouds exist only for a few Myr before forming stars. However, our analysis does not preclude that some molecular clouds persist considerably longer. If much of the star formation in spiral arms occurs within this short interval t H I24 μm, then star formation must be inefficient, in order to avoid the short-term depletion of the gas reservoir.

Journal ArticleDOI
TL;DR: The HI Nearby Galaxy Survey (THINGS) as discussed by the authors is a high spectral and spatial resolution survey of HI emission in 34 nearby galaxies obtained using the NRAO Very Large Array (VLA).
Abstract: We present "The HI Nearby Galaxy Survey (THINGS)", a high spectral (<=5.2 km/s) and spatial (~6") resolution survey of HI emission in 34 nearby galaxies obtained using the NRAO Very Large Array (VLA). The overarching scientific goal of THINGS is to investigate fundamental characteristics of the interstellar medium (ISM) related to galaxy morphology, star formation and mass distribution across the Hubble sequence. Unique characteristics of the THINGS database are the homogeneous sensitivity as well as spatial and velocity resolution of the HI data which is at the limit of what can be achieved with the VLA for a significant number of galaxies. A sample of 34 objects at distances 2

Journal ArticleDOI
TL;DR: In this paper, rotation curves of 19 galaxies from THINGS, The HI Nearby Galaxy Survey (THINGS) were used to derive the geometrical and dynamical parameters using HI data alone and combined with 3.6 um data from SINGS (Spitzer Infrared Nearby Galaxies Survey) to construct mass models.
Abstract: We present rotation curves of 19 galaxies from THINGS, The HI Nearby Galaxy Survey. The high spatial and velocity resolution of THINGS make these the highest quality HI rotation curves available to date for a large sample of nearby galaxies, spanning a wide range of HI masses and luminosities. The high quality of the data allows us to derive the geometrical and dynamical parameters using HI data alone. We do not find any declining rotation curves unambiguously associated with a cut-off in the mass distribution out to the last measured point. The rotation curves are combined with 3.6 um data from SINGS (Spitzer Infrared Nearby Galaxies Survey) to construct mass models. Our best-fit, dynamical disk masses, derived from the rotation curves, are in good agreement with photometric disk masses derived from the 3.6 um images in combination with stellar population synthesis arguments and two different assumptions for the stellar Initial Mass Function (IMF). We test the Cold Dark Matter-motivated cusp model, and the observationally motivated central density core model and find that (independent of IMF) for massive, disk-dominated galaxies, all halo models fit apparently equally well; for low-mass galaxies, however, a core-dominated halo is clearly preferred over a cuspy halo. The empirically derived densities of the dark matter halos of the late-type galaxies in our sample are half of what is predicted by CDM simulations, again independent of the assumed IMF.

Journal ArticleDOI
TL;DR: In this article, high-resolution (0.3") Very Large Array imaging of the molecular gas in the host galaxy of the high-redshift quasar PSS J2322+1944 (z = 4.12) is presented.
Abstract: We present high-resolution (0.3") Very Large Array imaging of the molecular gas in the host galaxy of the high-redshift quasar PSS J2322+1944 (z = 4.12). These observations confirm that the molecular gas (CO) in the host galaxy of this quasar is lensed into a full Einstein ring and reveal the internal gas dynamics in this system. The ring has a diameter of ~1.5" and thus is sampled over ~ 20 resolution elements by our observations. Through a model-based lens inversion, we recover the velocity gradient of the molecular reservoir in the quasar host galaxy of PSS J2322+1944. The Einstein ring lens configuration enables us to zoom in on the emission and to resolve scales down to ≾ 1 kpc. From the model-reconstructed source, we find that the molecular gas is distributed on a scale of 5 kpc and has a total mass of M(H_2) = 1.7 x 10^10 M⊙. A basic estimate of the dynamical mass gives M_(dyn) = 4.4 x 10^10 sin^-2 iM⊙, that is, only ~2.5 times the molecular gas mass and ~30 times the black hole mass (assuming that the dynamical structure is highly inclined). The lens configuration also allows us to tie the optical emission to the molecular gas emission, which suggests that the active galactic nucleus does reside within, but not close to the center of, the molecular reservoir. Together with the (at least partially) disturbed structure of the CO, this suggests that the system is interacting. Such interaction, possibly caused by a major "wet" merger, may be responsible for both feeding the quasar and fueling the massive starburst of 680 M⊙ yr^-1 in this system, in agreement with recently suggested scenarios of quasar activity and galaxy assembly in the early universe.

Journal ArticleDOI
TL;DR: In this article, high-resolution Very Large Array imaging of the molecular gas in the host galaxy of the highredshift quasar BRI 1335-0417 (z = 4.41) was presented.
Abstract: We present high-resolution Very Large Array imaging of the molecular gas in the host galaxy of the highredshift quasar BRI 1335-0417 (z = 4.41). Our CO(J = 2 → 1) observations have a linear resolution of 0.15" (1.0 kpc) and resolve the molecular gas emission both spatially and in velocity. The molecular gas in BRI 1335-0417 is extended on scales of 5 kpc, and shows a complex structure. At least three distinct components encompassing about two-thirds of the total molecular mass of 9.2 x 10^10⊙ are identified in velocity space, which are embedded in a structure that harbors about one-third of the total molecular mass in the system. The brightest CO(J = 2 → 1) line emission region has a peak brightness temperature of 61 ± 9 K within 1 kpc diameter, which is comparable to the kinetic gas temperature as predicted from the CO line excitation. This is also comparable to the gas temperatures found in the central regions of nearby ultraluminous infrared galaxies, which are however much more compact than 1 kpc. The spatial and velocity structure of the molecular reservoir in BRI 1335-0417 is inconsistent with a simple gravitationally bound disk, but resembles a merging system. Our observations are consistent with a major, gas-rich (“wet”) merger that both feeds an accreting supermassive black hole (causing the bright quasar activity), and fuels a massive starburst that builds up the stellar bulge in this galaxy. Our study of this z > 4 quasar host galaxy may thus be the most direct observational evidence that wet mergers at high redshift are related to AGN activity.

Journal ArticleDOI
TL;DR: In this article, a practical evaluation of the multi-scale CLEAN algorithm is presented and the results of this comparison show that several of the well-known characteristics and issues of using classical CLEAN are significantly lessened (or eliminated completely) when using the multiscale CLEAN.
Abstract: A practical evaluation of the multi-scale CLEAN algorithm is presented The data used in the comparisons are taken from The H I Nearby Galaxy Survey The implementation of multi-scale CLEAN in the CASA software package is used, although comparisons are made against the very similar multi-resolution CLEAN algorithm implemented in AIPS Both are compared against the classical CLEAN algorithm (as implemented in AIPS) The results of this comparison show that several of the well-known characteristics and issues of using classical CLEAN are significantly lessened (or eliminated completely) when using the multi-scale CLEAN algorithm Importantly, multi-scale CLEAN significantly reduces the effects of the clean "bowl" that is caused by missing short-spacings, and the "pedestal" of low-level un-cleaned flux (which affects flux scales and resolution) Multi-scale CLEAN can clean down to the noise level without the divergence suffered by classical CLEAN We discuss practical applications of the added contrast provided by multi-scale CLEAN using two selected astronomical examples: H I holes in the interstellar medium and anomalous gas structures outside the main galactic disk

01 Jan 2008
TL;DR: The H I Nearby Galaxy Survey (THINGS) as discussed by the authors is a high spectral (≤5.2 km s−1) and spatial (6'') resolution survey of H I emission in 34 nearby galaxies obtained using the NRAO Very Large Array (VLA).
Abstract: We present The H I Nearby Galaxy Survey (THINGS), a high spectral (≤5.2 km s–1) and spatial (~6'') resolution survey of H I emission in 34 nearby galaxies obtained using the NRAO Very Large Array (VLA). The overarching scientific goal of THINGS is to investigate fundamental characteristics of the interstellar medium (ISM) related to galaxy morphology, star formation, and mass distribution across the Hubble sequence. Unique characteristics of the THINGS database are the homogeneous sensitivity as well as spatial and velocity resolution of the H I data, which is at the limit of what can be achieved with the VLA for a significant number of galaxies. A sample of 34 objects at distances 2 D 15 Mpc (resulting in linear resolutions of ~100 to 500 pc) are targeted in THINGS, covering a wide range of star formation rates (~10–3 to 6 M ☉ yr–1), total H I masses M HI (0.01 to 14 × 109 M ☉), absolute luminosities M B (–11.5 to –21.7 mag), and metallicities (7.5 to 9.2 in units of 12+log[O/H]). We describe the setup of the VLA observations, the data reduction procedures, and the creation of the final THINGS data products. We present an atlas of the integrated H I maps, the velocity fields, the second moment (velocity dispersion) maps and individual channel maps of each THINGS galaxy. The THINGS data products are made publicly available through a dedicated webpage. Accompanying THINGS papers (in this issue of the Astronomical Journal) address issues such as the small-scale structure of the ISM, the (dark) matter distribution in THINGS galaxies, and the processes leading to star formation.

Journal ArticleDOI
TL;DR: In this article, the authors obtained a position (at subarcsecond accuracy) of the submillimeter bright source GOODS 850-5 (also known as GN 10) in the GOODS-North field using the IRAM Plateau de Bure interferometer at 1.25 mm wavelengths.
Abstract: We have obtained a position (at subarcsecond accuracy) of the submillimeter bright source GOODS 850-5 (also known as GN 10) in the GOODS-North field using the IRAM Plateau de Bure interferometer at 1.25 mm wavelengths (MM J123633+6214.1; flux density: -->S1.25 mm = 5.0 ± 1.0 mJy). This source has no optical counterpart in deep ACS imaging down to a limiting magnitude of i -->775 = 28.4 mag and its position is coincident with the position found in recent submillimeter mapping obtained at the SMA. Using deep VLA imaging at 20 cm, we find a radio source ( -->S20 cm = 34.4 ± 4.2 μJy) at the same position that is significantly brighter than reported by Wang and coworkers (but in agreement with a 3 σ detection previously reported by Pope and coworkers). The source is detected by Spitzer in IRAC as well as at 24 μm. We apply different photometric redshift estimators using measurements of the dusty, mid/far-infrared part of the SED and derive a redshift -->z ~ 4. Given our detection in the millimeter and radio we consider a significantly higher redshift (e.g., -->z ~ 6 recently proposed by Wang and coworkers) unlikely. MM J123633+6214.1 alias GOODS 850-5 nevertheless constitutes a bright representative of the high-redshift tail of the submillimeter galaxy population that may contribute a significant fraction to the (sub)millimeter background.

Journal ArticleDOI
TL;DR: In this paper, a practical evaluation of the Multi-Scale CLEAN algorithm is presented, and the results of this comparison show that several of the well-known characteristics and issues of using classical CLEAN are significantly lessened (or eliminated completely) when using the multi-scaleCLEAN algorithm.
Abstract: A practical evaluation of the Multi-Scale CLEAN algorithm is presented. The data used in the comparisons are taken from The HI Nearby Galaxy Survey (THINGS). The implementation of Multi-Scale CLEAN in the CASA software package is used, although comparisons are made against the very similar Multi-Resolution CLEAN algorithm implemented in AIPS. Both are compared against the classical CLEAN algorithm (as implemented in AIPS). The results of this comparison show that several of the well-known characteristics and issues of using classical CLEAN are significantly lessened (or eliminated completely) when using the Multi-Scale CLEAN algorithm. Importantly, Multi-Scale CLEAN reduces significantly the effects of the clean `bowl' caused by missing short-spacings, and the `pedestal' of low-level un-cleaned flux (which affects flux scales and resolution). Multi-Scale CLEAN can clean down to the noise level without the divergence suffered by classical CLEAN. We discuss practical applications of the added contrast provided by Multi-Scale CLEAN using two selected astronomical examples: HI holes in the interstellar medium and anomalous gas structures outside the main galactic disk.

Journal ArticleDOI
TL;DR: In this article, the authors presented observations of four z ≥ 5 SDSS quasars at 350 μm with the SHARC-II bolometer camera on the Caltech Submillimeter Observatory.
Abstract: We present observations of four z ≥ 5 SDSS quasars at 350 μm with the SHARC-II bolometer camera on the Caltech Submillimeter Observatory. These are among the deepest observations that have been made by SHARC-II at 350 μm, and three quasars are detected at ≥3σ significance, greatly increasing the sample of 350 μm (corresponds to rest frame wavelengths of <60 μm at z ≥ 5), detected high-redshift quasars. The derived rest frame far-infrared (FIR) emission in the three detected sources is about five to ten times stronger than that expected from the average spectral energy distribution (SED) of the local quasars given the same 1450 A luminosity. Combining the previous submillimeter and millimeter observations at longer wavelengths, the temperatures of the FIR-emitting warm dust from the three quasar detections are estimated to be in the range of 39-52 K. Additionally, the FIR-to-radio SEDs of the three 350 μm detections are consistent with the emission from typical star-forming galaxies. The FIR luminosities are ~1013 L ☉ and the dust masses are ≥108 M ☉. These results confirm that huge amounts of warm dust can exist in the host galaxies of optically bright quasars as early as z ~ 6. The universe is so young at these epochs (~1 Gyr) that a rapid dust-formation mechanism is required. We estimate the size of the FIR dust-emission region to be about a few kpc, and further provide a comparison of the SEDs among different kinds of dust-emitting sources to investigate the dominant dust-heating mechanism.

Journal ArticleDOI
TL;DR: In this paper, the authors used the Spitzer Infrared Array Camera (IRAC) observations of two fields in the extended UV disk (XUV-disk) of M83 to constrain stellar masses and ages of the UV clumps in the fields.
Abstract: Spitzer Infrared Array Camera (IRAC) observations of two fields in the extended UV disk (XUV-disk) of M83 have been recently obtained, ~3 R HII away from the center of the galaxy (R HII = 6.6 kpc). Galaxy Evolution Explorer (GALEX) UV images have shown the two fields to host in situ recent star formation. The IRAC images are used in conjunction with GALEX data and new H I imaging from The H I Nearby Galaxy Survey (THINGS) to constrain stellar masses and ages of the UV clumps in the fields, and to relate the local recent star formation to the reservoir of available gas. Multi-wavelength photometry in the UV and mid-IR (MIR) bands of 136 UV clumps (spatial resolution >220 pc) identified in the two target fields, together with model fitting of the stellar UV-MIR spectral energy distributions (SEDs), suggests that the clumps cover a range of ages between a few Myr and >1 Gyr with a median value around ≤100 Myr, and have masses in the range 103-3 × 106 M ☉, with a peak . The range of observed ages, for which only a small fraction of the mass in stars appears to have formed in the past ~10 Myr, agrees with the dearth of Hα emission observed in these outer fields. At the location of our IRAC fields, the H I map shows localized enhancement and clumping of atomic gas. A comparison of the observed star formation with the gas reservoir shows that the UV clumps follow the Schmidt-Kennicutt scaling law of star formation, and that star formation is occurring in regions with gas densities at approximately (within a factor of a few) the critical density value derived according to the Toomre Q gravitational stability criterion. The significant 8 μm excess in several of the clumps (16% of the total by number accounting for ~67% of the 8 μm flux) provides evidence for the existence of dust in these remote fields, in agreement with results for other galaxies. Furthermore, we observe a relatively small excess of emission at 4.5 μm in the clumps (14% ± 6% by flux), which suggests contribution from hot small grains (~1000 K), as already observed in other galaxies. From our data, the outer regions of the M83 galaxy disk show evidence of a time-extended star-formation history over 1 Gyr, and of a moderately chemically-evolved interstellar medium, in agreement with recent findings on the metallicity of the outer H II regions of M83.

Journal ArticleDOI
TL;DR: In this paper, the authors estimate a conservative upper limit on the mass of molecular gas within 100 pc and ±400 km s−1 line-of-sight velocity of the central black hole of the giant elliptical galaxy M87, including an allowance for possible systematic errors associated with subtraction of the continuum.
Abstract: Supermassive black holes in giant elliptical galaxies are remarkably faint given their expected accretion rates. This motivates models of radiatively inefficient accretion due to either ion-electron thermal decoupling, generation of outflows that inhibit accretion, or settling of gas to a gravitationally unstable disk that forms stars in preference to feeding the black hole. The latter model predicts the presence of cold molecular gas in a thin disk around the black hole. Here we report Submillimeter Array observations of the nucleus of the giant elliptical galaxy M87 that probe 230 GHz continuum and CO (J = 2–1) line emission. Continuum emission is detected from the nucleus and several knots in the jet, including one that has been undergoing flaring behavior. We estimate a conservative upper limit on the mass of molecular gas within ~100 pc and ±400 km s−1 line-of-sight velocity of the central black hole of ~8 × 106 M☉, which includes an allowance for possible systematic errors associated with subtraction of the continuum. Ignoring such errors, we have a 3 σ sensitivity to ~3 × 106 M☉. In fact, the continuum-subtracted spectrum shows weak emission features extending up to 4 σ above the rms dispersion of the line-free channels. These may be artifacts of the continuum subtraction process. Alternatively, if they are interpreted as CO emission, then the implied molecular gas mass is ~5 × 106 M☉ spread out over a velocity range of 700 km s−1. These constraints on molecular gas mass are close to the predictions of the model of self-gravitating, star-forming accretion disks fed by Bondi accretion (Tan & Blackman 2005).

Journal ArticleDOI
TL;DR: In this paper, the authors used deep imaging from the Advanced Camera for Surveys aboard the Hubble Space Telescope (HST) to measure the star formation history of a region including the SGS, focusing on the past 500 Myr, and employ the unique properties of blue helium burning stars to create a movie of star formation in the supergiant HI shell.
Abstract: Based on deep imaging from the Advanced Camera for Surveys aboard the Hubble Space Telescope, we present new evidence that stellar feedback created a ~ 1 kpc supergiant HI shell (SGS) and triggered star formation (SF) around its rim in the M81 Group dwarf irregular galaxy IC 2574. Using photometry of the resolved stars from the HST images, we measure the star formation history of a region including the SGS, focusing on the past 500 Myr, and employ the unique properties of blue helium burning stars to create a movie of SF in the SGS. We find two significant episodes of SF inside the SGS from 200 - 300 Myr and ~ 25 Myr ago. Comparing the timing of the SF events to the dynamic age of the SGS and the energetics from the HI and SF, we find compelling evidence that stellar feedback is responsible for creating the SGS and triggering secondary SF around its rim.

Journal ArticleDOI
TL;DR: In this article, the velocity width of neutral gas in damped Lyα (DLA) systems are inconsistent with these systems originating in gas disks of galaxies, similar to those seen in the local universe.
Abstract: We demonstrate in this paper that the velocity widths of the neutral gas in damped Lyα (DLA) systems are inconsistent with these systems originating in gas disks of galaxies, similar to those seen in the local universe. We examine the gas kinematics of local galaxies using the high-quality H I 21 cm data from the H I Nearby Galaxies Survey and make a comparison with the velocity profiles measured in the low-ionization metal lines observed in DLAs at high redshifts. The median velocity width of z = 0 H I gas above the DLA column density limit of N H I = 2 × 1020 cm–2 is approximately 30 km s–1, whereas the typical value in DLAs is a factor of 2 higher. We argue that the gas kinematics at higher redshifts are increasingly influenced by gas that is not participating in ordered rotation in cold disks, but is more likely associated with tidal gas related to galaxy interactions or processes such as superwinds and outflows. An analysis of the H I in the local interacting starburst galaxy M 82 shows that the velocity widths in this galaxy are indeed similar to what is seen in DLAs.

Journal ArticleDOI
TL;DR: Using the IRAM 30 m telescope and the Plateau de Bure interferometer, this article detected the C I((3)P(2) -> (3) P(1)) and the CO 3-2, 4-3, 6-5, 7-6 transitions as well as the dust continuum at 3 and 1.2 mm towards distant luminous infrared galaxy IRAS F10214+4724 at z = 2.286.
Abstract: Using the IRAM 30 m telescope and the Plateau de Bure interferometer we have detected the C I((3)P(2) -> (3)P(1)) and the CO 3-2, 4-3, 6-5, 7-6 transitions as well as the dust continuum at 3 and 1.2 mm towards the distant luminous infrared galaxy IRAS F10214+4724 at z = 2.286. The C I((3)P(2) -> (3)P(1)) line is detected for the first time towards this source and IRAS F10214+4724 now belongs to a sample of only 3 extragalactic sources at any redshift where both of the carbon fine structure lines have been detected. The source is spatially resolved by our C I((3)P(2) -> (3)P(1)) observation and we detect a velocity gradient along the east-west direction. The CI line ratio allows us to derive a carbon excitation temperature of 42(-9)(+12) K. The carbon excitation in conjunction with the CO ladder and the dust continuum constrain the gas density to n(H(2)) = 10(3.6-4.0) cm(-3) and the kinetic temperature to T(kin) = 45-80 K, similar to the excitation conditions found in nearby starburst galaxies. The rest-frame 360 mu m dust continuum morphology is more compact than the line emitting region, which supports previous findings that the far infrared luminosity arises from regions closer to the active galactic nucleus at the center of this system.

Journal ArticleDOI
TL;DR: In this article, the authors presented a sensitive search for the ground state fine structure line at 205 microns of ionized nitrogen (NII) in one of the highest redshift quasars (J1148+5251 at z=6.42) using the IRAM 30m telescope.
Abstract: We present a sensitive search for the ^3P_1->^3P_0 ground state fine structure line at 205 microns of ionized nitrogen ([NII]) in one of the highest redshift quasars (J1148+5251 at z=6.42) using the IRAM 30m telescope. The line is not detected at a (3 sigma) depth of 0.47 Jy km s^-1, corresponding to a [NII] luminosity limit of L_[NII] 7) using the Atacama Large Millimeter/submillimeter Array (ALMA), for which the highly excited rotational transitions of CO will be shifted outside the accessible (sub-)millimeter bands.