Showing papers by "Fabian Walter published in 2009"

Heracles: the hera co line extragalactic survey

Abstract: Original article can be found at: http://www.iop.org/EJ/journal/1538-3881 Copyright American Astronomical Society. DOI: 10.1088/0004-6256/137/6/4670 [Full text of this article is not available in the UHRA]

COMPARISON OF Hα AND UV STAR FORMATION RATES IN THE LOCAL VOLUME: SYSTEMATIC DISCREPANCIES FOR DWARF GALAXIES

Abstract: Using a complete sample of ~300 star-forming galaxies within 11 Mpc of the Milky Way, we evaluate the consistency between star formation rates (SFRs) inferred from the far ultraviolet (FUV) non-ionizing continuum and Hα nebular emission, assuming standard conversion recipes in which the SFR scales linearly with luminosity at a given wavelength. Our analysis probes SFRs over 5 orders of magnitude, down to ultra-low activities on the order of ~10^–4 M_☉ yr^–1. The data are drawn from the 11 Mpc Hα and Ultraviolet Galaxy Survey (11HUGS), which has obtained Hα fluxes from ground-based narrowband imaging, and UV fluxes from imaging with GALEX. For normal spiral galaxies (SFR ~ 1 M_☉ yr^–1), our results are consistent with previous work which has shown that FUV SFRs tend to be lower than Hα SFRs before accounting for internal dust attenuation, but that there is relative consistency between the two tracers after proper corrections are applied. However, a puzzle is encountered at the faint end of the luminosity function. As lower luminosity dwarf galaxies, roughly less active than the Small Magellanic Cloud, are examined, Hα tends to increasingly underpredict the total SFR relative to the FUV. The trend is evident prior to corrections for dust attenuation, which affects the FUV more than the nebular Hα emission, so this general conclusion is robust to the effects of dust. Although past studies have suggested similar trends, this is the first time this effect is probed with a statistical sample for galaxies with SFR ≤0.1 M_☉ yr^–1. By SFR ~ 0.003 M_☉ yr–1, the average Hα-to-FUV flux ratio is lower than expected by a factor of two, and at the lowest SFRs probed, the ratio exhibits an order of magnitude discrepancy for the handful of galaxies that remain in the sample. A range of standard explanations does not appear to be able to fully account for the magnitude of the systematic. Some recent work has argued for a stellar initial mass function which is deficient in high-mass stars in dwarf and low surface brightness galaxies, and we also consider this scenario. Under the assumption that the FUV traces the SFR in dwarf galaxies more robustly, the prescription relating Hα luminosity to SFR is re-calibrated for use in the low SFR regime when FUV data are not available.

The spitzer local volume legacy: survey description and infrared photometry

Abstract: The survey description and the near-, mid-, and far-infrared flux properties are presented for the 258 galaxies in the Local Volume Legacy (LVL). LVL is a Spitzer Space Telescope legacy program that surveys the local universe out to 11 Mpc, built upon a foundation of ultraviolet, Hα, and Hubble Space Telescope imaging from 11HUGS (11 Mpc Hα and Ultraviolet Galaxy Survey) and ANGST (ACS Nearby Galaxy Survey Treasury). LVL covers an unbiased, representative, and statistically robust sample of nearby star-forming galaxies, exploiting the highest extragalactic spatial resolution achievable with Spitzer. As a result of its approximately volume-limited nature, LVL augments previous Spitzer observations of present-day galaxies with improved sampling of the low-luminosity galaxy population. The collection of LVL galaxies shows a large spread in mid-infrared colors, likely due to the conspicuous deficiency of 8 μm polycyclic aromatic hydrocarbon emission from low-metallicity, low-luminosity galaxies. Conversely, the far-infrared emission tightly tracks the total infrared emission, with a dispersion in their flux ratio of only 0.1 dex. In terms of the relation between the infrared-to-ultraviolet ratio and the ultraviolet spectral slope, the LVL sample shows redder colors and/or lower infrared-to-ultraviolet ratios than starburst galaxies, suggesting that reprocessing by dust is less important in the lower mass systems that dominate the LVL sample. Comparisons with theoretical models suggest that the amplitude of deviations from the relation found for starburst galaxies correlates with the age of the stellar populations that dominate the ultraviolet/optical luminosities.

Comparison of H-alpha and UV Star Formation Rates in the Local Volume: Systematic Discrepancies for Dwarf Galaxies

Abstract: (abridged) Using a complete sample of ~300 star-forming galaxies within 11 Mpc, we evaluate the consistency between star formation rates (SFRs) inferred from the far ultraviolet (FUV) non-ionizing continuum and H-alpha nebular emission, assuming standard conversion recipes in which the SFR scales linearly with luminosity at a given wavelength. Our analysis probes SFRs over 5 orders of magnitude, down to ultra-low activities on the order of ~0.0001 M_sun/yr. The data are drawn from the 11 Mpc H-alpha and Ultraviolet Galaxy Survey (11HUGS), which has obtained H-alpha fluxes from ground-based narrowband imaging, and UV fluxes from imaging with GALEX. For normal spiral galaxies (SFR~1 M_sun/yr), our results are consistent with previous work which has shown that FUV SFRs tend to be lower than H-alpha SFRs before accounting for internal dust attenuation, but that there is relative consistency between the two tracers after proper corrections are applied. However, a puzzle is encountered at the faint end of the luminosity function. As lower luminosity dwarf galaxies, roughly less active than the Small Magellanic Cloud, are examined, H-alpha tends to increasingly under-predict the SFR relative to the FUV. Although past studies have suggested similar trends, this is the first time this effect is probed with a statistical sample for galaxies with SFR~<0.1 M_sun/yr. A range of standard explanations does not appear to be able to account for the magnitude of the systematic. Some recent work has argued for an IMF which is deficient in high mass stars in dwarf and low surface brightness galaxies, and we also consider this scenario.

The Large Apex Bolometer Camera Survey of the Extended Chandra Deep Field South

Abstract: We present a sensitive 870 mum survey of the Extended Chandra Deep Field South (ECDFS) combining 310 hr of observing time with the Large Apex BOlometer Camera (LABOCA) on the APEX telescope. The LABOCA ECDFS Submillimetre Survey (LESS) covers the full 30' x 30' field size of the ECDFS and has a uniform noise level of sigma{sub 870{sub m}}u{sub m} approx 1.2 mJy beam{sup -1}. LESS is thus the largest contiguous deep submillimeter survey undertaken to date. The noise properties of our map show clear evidence that we are beginning to be affected by confusion noise. We present a catalog of 126 submillimeter galaxies (SMGs) detected with a significance level above 3.7sigma, at which level we expect five false detections given our map area of 1260 arcmin{sup 2}. The ECDFS exhibits a deficit of bright SMGs relative to previously studied blank fields but not of normal star-forming galaxies that dominate the extragalactic background light (EBL). This is in line with the underdensities observed for optically defined high redshift source populations in the ECDFS (BzKs, DRGs, optically bright active galactic nucleus, and massive K-band-selected galaxies). The differential source counts in the full field are well described by a power law withmore » a slope of alpha = -3.2, comparable to the results from other fields. We show that the shape of the source counts is not uniform across the field. Instead, it steepens in regions with low SMG density. Towards the highest overdensities we measure a source-count shape consistent with previous surveys. The integrated 870 mum flux densities of our source-count models down to S{sub 870{sub m}}u{sub m} = 0.5 mJy account for >65% of the estimated EBL from COBE measurements. We have investigated the clustering of SMGs in the ECDFS by means of a two-point correlation function and find evidence for strong clustering on angular scales <1' with a significance of 3.4sigma. Assuming a power-law dependence for the correlation function and a typical redshift distribution for the SMGs we derive a characteristic angular clustering scale of theta{sub 0} = 14'' +- 7'' and a spatial correlation length of r{sub 0} = 13 +- 6 h {sup -1} Mpc.« less

What is driving the h i velocity dispersion

Abstract: Original article can be found at: http://www.iop.org/EJ/journal/1538-3881 Copyright American Astronomical Society. DOI: 10.1088/0004-6256/137/5/4424 [Full text of this article is not available in the UHRA]

What is Driving the HI Velocity Dispersion

Abstract: We explore what dominant physical mechanism sets the kinetic energy contained in neutral, atomic (HI) gas. We compare the HI line widths predicted from turbulence driven by supernova (SN) explosions and magneto-rotational instability (MRI) to direct observations in 11 disk galaxies. We use high-quality maps of the HI mass surface density and line width, obtained by the THINGS survey. We show that all sample galaxies exhibit a systematic radial decline in the HI line width, which appears to be a generic property of HI disks and also implies a radial decline in kinetic energy density of HI. At a galactocentric radius of r25 there is a characteristic value of the HI velocity dispersion of $10\pm2$ \kms. Inside this radius, galaxies show HI line widths above the thermal value expected from a warm HI component, implying that turbulence drivers must be responsible for maintaining this line width. Therefore, we compare maps of HI kinetic energy to maps of the star formation rate (SFR) and to predictions for energy generated by MRI. We find a positive correlation between kinetic energy of HI and SFR. For a given turbulence dissipation timescale we can estimate the energy input required to maintain the observed kinetic energy. The SN rate implied by the observed recent SFR is sufficient to maintain the observed velocity dispersion, if the SN feedback efficiency is at least \epsilon_SN\simeq0.1. Beyond r25, this efficiency would have to increase to unrealistic values, $\epsilon>1$, suggesting that mechanical energy from young stars does not supply most energy in outer disks. On the other hand, both thermal broadening and turbulence driven by MRI can produce the velocity dispersions and kinetic energies that we observe in this regime.

A kiloparsec-scale hyper-starburst in a quasar host less than 1 gigayear after the Big Bang

Abstract: The host galaxy of the quasar SDSS J114816.64+1525150.3 (at redshift z=6.42, when the Universe was less than a billion years old) has an infrared luminosity of 2.2 x 10^(13) times that of the Sun, presumably significantly powered by a massive burst of star formation. In local examples of extremely luminous galaxies, such as Arp 220, the burst of star formation is concentrated in a relatively small central region of <100 pc radius. It is not known on which scales stars are forming in active galaxies in the early Universe, at a time when they are probably undergoing their initial burst of star formation. We do know that at some early time, structures comparable to the spheroidal bulge of the Milky Way must have formed. Here we report a spatially resolved image of [C II] emission of the host galaxy of J114816.64+1525150.3 that demonstrates that its star-forming gas is distributed over a radius of about 750 pc around the centre. The surface density of the star formation rate averaged over this region is ~1,000M⊙[year^(-1) kpc^(-2). This surface density is comparable to the peak in Arp 220, although about two orders of magnitude larger in area. This vigorous star-forming event is likely to give rise to a massive spheroidal component in this system.

LOW MILKY-WAY-LIKE MOLECULAR GAS EXCITATION OF MASSIVE DISK GALAXIES AT z ∼ 1.5

Abstract: We present evidence for Milky-Way-like, low-excitation molecular gas reservoirs in near-IR-selected massive galaxies at z ~ 1.5, based on IRAM Plateau de Bure Interferometer CO[3-2] and NRAO Very Large Array CO[1-0] line observations for two galaxies that had been previously detected in CO[2-1] emission. The CO[3-2] flux of BzK – 21000 at z = 1.522 is comparable within the errors to its CO[2-1] flux, implying that the CO[3-2] transition is significantly subthermally excited. The combined CO[1-0] observations of the two sources result in a detection at the 3σ level that is consistent with a higher CO[1-0] luminosity than that of CO[2-1]. Contrary to what is observed in submillimeter galaxies and quasi-stellar objects, in which the CO transitions are thermally excited up to J ≥ 3, these galaxies have low-excitation molecular gas, similar to that in the Milky Way and local spirals. This is the first time that such conditions have been observed at high redshift. A Large Velocity Gradient analysis suggests that molecular clouds with density and kinetic temperature comparable to local spirals can reproduce our observations. The similarity in the CO excitation properties suggests that a high, Milky-Way-like, CO to H2 conversion factor could be appropriate for these systems. If such low-excitation properties are representative of ordinary galaxies at high redshift, centimeter telescopes such as the Expanded Very Large Array and the longest wavelength Atacama Large Millimeter Array bands will be the best tools for studying the molecular gas content in these systems through the observations of CO emission lines.

A CO Emission Line from the Optical and Near-IR Undetected Submillimeter Galaxy GN10

Abstract: We report the detection of a CO emission line from the submillimiter galaxy (SMG) GN10 in the GOODS-N field. GN10 lacks any counterpart in extremely deep optical a nd near-IR imaging obtained with the Hubble Space Telescope and ground-based facilities. This is a prototypical case of a source that is extremely obscured by dust, for which it is practically impossible to derive a sp ectroscopic redshift in the optical/near-IR. Under the hypothesis that GN10 is part of a proto-cluster structur e previously identified at z ∼ 4.05 in the same field, we searched for CO[4-3] at 91.4 GHz with the IRAM Plateau de Bure Interferometer, and successfully detected a line. We find that the most likely redshift identification is z = 4.0424 ± 0.0013, based on: 1) the very low chance that the CO line is actually serendipitous from a different redshift; 2) a radio-IR photometric redshift analysis; 3) the identical radio-IR SED, within a scaling fa ctor, of two other SMGs at the same redshift. The faintness at optical/near-IR wavelengths requires an atte nuation of AV ∼ 5‐7.5 mag. This result supports the case that a substantial population of very high-z SMGs exists that had been missed by previous spectroscopic surveys. This is the first time that a CO emission line has been detected for a galaxy that is invisible in the optical and near-IR. Our work demonstrates the power of existing and planned facilities for completing the census of star formation and stellar mass in the distant Universe by measuring redshifts of the most obscured galaxies through millimeter spectroscopy. Subject headings:galaxies: formation — cosmology: observations — infrared: galaxies — galaxies: starburst — galaxies: high-redshift — submillimeter

A submillimetre galaxy at z = 4.76 in the LABOCA survey of the Extended Chandra Deep Field-South

Abstract: We report on the identification of the highest redshift submillimetre-selected source currently known LESS J033229.4−275619. This source was detected in the Large Apex Bolometer Camera (LABOCA) Extended Chandra Deep Field-South (ECDF-S) Submillimetre Survey (LESS), a sensitive 870-μm survey (σ_(870 μm)∼ 1.2 mJy) of the full 30 × 30 arcmin_2 ECDF-S with the LABOCA on the Atacama Pathfinder Experiment telescope. The submillimetre emission is identified with a radio counterpart for which optical spectroscopy provides a redshift of z= 4.76 . We show that the bolometric emission is dominated by a starburst with a star formation rate of ∼1000 M_⊙ yr^(−1), although we also identify a moderate luminosity active galactic nucleus (AGN) in this galaxy. Thus it has characteristics similar to those of z∼ 2 submillimetre galaxies (SMGs), with a mix of starburst and obscured AGN signatures. This demonstrates that ultraluminous starburst activity is not just restricted to the hosts of the most luminous (and hence rare) quasi-stellar objects at z∼ 5 , but was also occurring in less extreme galaxies at a time when the Universe was less than 10 per cent of its current age. Assuming that we are seeing the major phase of star formation in this galaxy, then we demonstrate that it would be identified as a luminous distant red galaxy at z∼ 3 and that the current estimate of the space density of z > 4 SMGs is only sufficient to produce ≳10 per cent of the luminous red galaxy population at these early times. However, this leaves open the possibility that some of these galaxies formed through less intense, but more extended star formation events. If the progenitors of all of the luminous red galaxies at z∼ 3 go through an ultraluminous starburst at z≳ 4 then the required volume density of z > 4 SMGs will exceed that predicted by current galaxy formation models by more than an order of magnitude.

A submillimetre galaxy at z=4.76 in the LABOCA survey of the Extended Chandra Deep Field South

Abstract: We report on the identification of the highest redshift submm-selected source currently known: LESSJ033229.4-275619. This source was detected in the Large Apex BOlometer CAmera (LABOCA) Extended Chandra Deep Field South (ECDFS) Submillimetre Survey (LESS), a sensitive 870-um survey (~1.2-mJy rms) of the full 30'x30' ECDFS with the LABOCA camera on the Atacama Pathfinder EXperiment (APEX) telescope. The submm emission is identified with a radio counterpart for which optical spectroscopy provides a redshift of z=4.76. We show that the bolometric emission is dominated by a starburst with a star formation rate of ~1000 Msun/yr, although we also identify a moderate luminosity Active Galactic Nucleus (AGN) in this galaxy. Thus it has characteristics similar to those of z~2 submm galaxies (SMGs), with a mix of starburst and obscured AGN signatures. This demonstrates that ultraluminous starburst activity is not just restricted to the hosts of the most luminous (and hence rare) QSOs at z~5, but was also occurring in less extreme galaxies at a time when the Universe was less than 10% of its current age. Assuming that we are seeing the major phase of star formation in this galaxy, then we demonstrate that it would be identified as a luminous distant red galaxy at z~3 and that the current estimate of the space density of z>4 SMGs is only sufficient to produce ~10% of the luminous red galaxy population at these early times. However, this leaves open the possibility that some of these galaxies formed through less intense, but more extended star formation events. If the progenitors of all of the luminous red galaxies at z~3 go through an ultraluminous starburst at z>4 then the required volume density of z>4 SMGs will exceed that predicted by current galaxy formation models by more than an order of magnitude.

BLAST: the far-infrared/radio correlation in distant galaxies

Abstract: We investigate the correlation between far-infrared (FIR) and radio luminosities in distant galaxies, a lynchpin of modern astronomy. We use data from the Balloon-borne Large Aperture Submillimetre Telescope (BLAST), Spitzer, the Large Apex BOlometer CamerA (LABOCA), the Very Large Array (VLA) and the Giant Metre-wave Radio Telescope (GMRT) in the Extended Chandra Deep Field South (ECDFS). For a catalogue of BLAST 250-micron-selected galaxies, we re-measure the 70--870-micron flux densities at the positions of their most likely 24-micron counterparts, which have a median [interquartile] redshift of 0.74 [0.25, 1.57]. From these, we determine the monochromatic flux density ratio, q_250 = log_10 (S_250micron / S_1400MHz), and the bolometric equivalent, q_IR. At z ~= 0.6, where our 250-micron filter probes rest-frame 160-micron emission, we find no evolution relative to q_160 for local galaxies. We also stack the FIR and submm images at the positions of 24-micron- and radio-selected galaxies. The difference between q_IR seen for 250-micron- and radio-selected galaxies suggests star formation provides most of the IR luminosity in ~< 100-uJy radio galaxies, but rather less for those in the mJy regime. For the 24-micron sample, the radio spectral index is constant across 0 < z < 3, but q_IR exhibits tentative evidence of a steady decline such that q_IR is proportional to (1+z)^(-0.15 +/- 0.03) - significant evolution, spanning the epoch of galaxy formation, with major implications for techniques that rely on the FIR/radio correlation. We compare with model predictions and speculate that we may be seeing the increase in radio activity that gives rise to the radio background.

Imaging Atomic and Highly Excited Molecular Gas in a z = 6.42 Quasar Host Galaxy: Copious Fuel for an Eddington-limited Starburst at the End of Cosmic Reionization

Abstract: We have imaged CO(J = 7→6) and C i(^3P_2→^3P_1) emission in the host galaxy of the z = 6.42 quasar SDSS J114816.64+525150.3 (hereafter J1148+5251) through observations with the Plateau de Bure Interferometer. The region showing CO(J = 7→6) emission is spatially resolved, and its size of 5 kpc is in good agreement with earlier CO(J = 3→2) observations. In combination with a revised model of the collisional line excitation in this source, this indicates that the highly excited molecular gas traced by the CO J = 7→6 line is subthermally excited (showing only 58% ± 8% of the CO J = 3→2 luminosity), but not more centrally concentrated. We also detect Ci(^3P_2→^3P_1) emission in the host galaxy of J1148+5251, but the line is too faint to enable a reliable size measurement. From the C i(^3P_2→^3P_1) line flux, we derive a total atomic carbon mass of M_(Ci) = 1.1 ×10^7 M_⊙, which corresponds to ~5 × 10^(−4) times the total molecular gas mass. We also searched for H_2O(J_(K_aK_c) = 212→101) emission, and obtained a sensitive line luminosity limit of L'_(H_2O) < 4.4 × 10^9 K km s^(−1) pc^2, i.e., <15% of the CO(J = 3→2) luminosity. The warm, highly excited molecular gas, atomic gas and dust in this quasar host at the end of cosmic reionization maintain an intense starburst that reaches surface densities as high as predicted by (dust opacity) Eddington limited star formation over kiloparsec scales.

Low, Milky-Way like, Molecular Gas Excitation of Massive Disk Galaxies at z~1.5

Abstract: We present evidence for Milky-Way-like, low-excitation molecular gas reservoirs in near-IR selected massive galaxies at z~1.5, based on IRAM Plateau de Bure Interferometer CO[3-2] and NRAO Very Large Array CO[1-0] line observations for two galaxies that had been previously detected in CO[2-1] emission. The CO[3-2] flux of BzK-21000 at z=1.522 is comparable within the errors to its CO[2-1] flux, implying that the CO[3-2] transition is significantly sub-thermally excited. The combined CO[1-0] observations of the two sources result in a detection at the 3 sigma level that is consistent with a higher CO[1-0] luminosity than that of CO[2-1]. Contrary to what is observed in submillimeter galaxies and QSOs, in which the CO transitions are thermally excited up to J>=3, these galaxies have low-excitation molecular gas, similar to that in the Milky Way and local spirals. This is the first time that such conditions have been observed at high redshift. A Large Velocity Gradient analysis suggests that molecular clouds with density and kinetic temperature comparable to local spirals can reproduce our observations. The similarity in the CO excitation properties suggests that a high, Milky-Way-like, CO to H_2 conversion factor could be appropriate for these systems. If such low-excitation properties are representative of ordinary galaxies at high redshift, centimeter telescopes such as the Expanded Very Large Array and the longest wavelength Atacama Large Millimeter Array bands will be the best tools for studying the molecular gas content in these systems through the observations of CO emission lines.

A CO emission line from the optical and near-IR undetected submillimeter galaxy GN10

Abstract: We report the detection of a CO emission line from the submillimiter galaxy (SMG) GN10 in the GOODS-N field. GN10 lacks any counterpart in extremely deep optical and near-IR imaging obtained with the Hubble Space Telescope and ground-based facilities. This is a prototypical case of a source that is extremely obscured by dust, for which it is practically impossible to derive a spectroscopic redshift in the optical/near-IR. Under the hypothesis that GN10 is part of a proto-cluster structure previously identified at z~4.05 in the same field, we searched for CO[4-3] at 91.4 GHz with the IRAM Plateau de Bure Interferometer, and successfully detected a line. We find that the most likely redshift identification is z=4.0424+-0.0013, based on: 1) the very low chance that the CO line is actually serendipitous from a different redshift; 2) a radio-IR photometric redshift analysis; 3) the identical radio-IR SED, within a scaling factor, of two other SMGs at the same redshift. The faintness at optical/near-IR wavelengths requires an attenuation of A_V~5-7.5 mag. This result supports the case that a substantial population of very high-z SMGs exists that had been missed by previous spectroscopic surveys. This is the first time that a CO emission line has been detected for a galaxy that is invisible in the optical and near-IR. Our work demonstrates the power of existing and planned facilities for completing the census of star formation and stellar mass in the distant Universe by measuring redshifts of the most obscured galaxies through millimeter spectroscopy.

IMAGING THE MOLECULAR GAS IN A z = 3.9 QUASAR HOST GALAXY AT 0.″3 RESOLUTION: A CENTRAL, SUB-KILOPARSEC SCALE STAR FORMATION RESERVOIR IN APM 08279+5255

Abstract: We have mapped the molecular gas content in the host galaxy of the strongly lensed high-redshift quasar APM 08279+5255 (z = 3.911) with the Very Large Array at 0\farcs3 resolution. The CO(J = 1➝0) emission is clearly resolved in our maps. The CO(J = 1➝0) line luminosity derived from these maps is in good agreement with a previous single-dish measurement. In contrast to previous interferometer-based studies, we find that the full molecular gas reservoir is situated in two compact peaks separated by ≲0\farcs4. Our observations reveal, for the first time, that the emission from cold molecular gas is virtually co-spatial with the optical/near-infrared continuum emission of the central active galactic nucleus (AGN) in this source. This striking similarity in morphology indicates that the molecular gas is situated in a compact region close to the AGN. Based on the high-resolution CO maps, we present a revised model for the gravitational lensing in this system, which indicates that the molecular gas emission is magnified by only a factor of 4 (in contrast to previously suggested factors of 100). This model suggests that the CO is situated in a circumnuclear disk of ~550 pc radius that is possibly seen at an inclination of ≲25°, i.e., relatively close to face-on. From the CO luminosity, we derive a molecular gas mass of Mgas = 1.3x10^11 M☉ for this galaxy. From the CO structure and linewidth, we derive a dynamical mass of M dyn sin^2 i = 4.0x10^10 M☉. Based on a revised mass estimate for the central black hole of Mbh = 2.3x10^10 M☉ and the results of our molecular line study, we find that the mass of the stellar bulge of APM 08279+5255 falls short of the local M BH-σbulge relationship of nearby galaxies by more than an order of magnitude, lending support to recent suggestions that this relation may evolve with cosmic time and/or change toward the high-mass end.

Imaging Atomic and Highly Excited Molecular Gas in a z=6.42 Quasar Host Galaxy: Copious Fuel for an Eddington-Limited Starburst at the End of Cosmic Reionization

Abstract: We have imaged CO(J=7-6) and CI(3P2-3P1) emission in the host galaxy of the z=6.42 quasar SDSS J114816.64+525150.3 (hereafter: J1148+5251) through observations with the Plateau de Bure Interferometer. The region showing CO(J=7-6) emission is spatially resolved, and its size of 5 kpc is in good agreement with earlier CO(J=3-2) observations. In combination with a revised model of the collisional line excitation in this source, this indicates that the highly excited molecular gas traced by the CO J=7-6 line is subthermally excited (showing only 58+/-8% of the CO J=3-2 luminosity), but not more centrally concentrated. We also detect CI(3P2-3P1) emission in the host galaxy of J1148+5251, but the line is too faint to enable a reliable size measurement. From the CI(3P2-3P1) line flux, we derive a total atomic carbon mass of M_CI=1.1x10^7 M_sun, which corresponds to ~5x10^-4 times the total molecular gas mass. We also searched for H2O(J_KaKc=2_12-1_01) emission, and obtained a sensitive line luminosity limit of L'_H2O<4.4x10^9 K kms pc^2, i.e., <15% of the CO(J=3-2) luminosity. The warm, highly excited molecular gas, atomic gas and dust in this quasar host at the end of cosmic reionization maintain an intense starburst that reaches surface densities as high as predicted by (dust opacity) Eddington limited star formation over kiloparsec scales.

First redshift determination of an optically/UV faint submillimeter galaxy using CO emission lines

Abstract: We report the redshift of a distant, highly obscured submm galaxy (SMG), based entirely on the detection of its CO line emission We have used the newly commissioned Eight-MIxer Receiver (EMIR) at the IRAM 30m telescope, with its 8 GHz of instantaneous dual-polarization bandwidth, to search the 3-mm atmospheric window for CO emission from SMMJ14009+0252, a bright SMG detected in the SCUBA Lens Survey A detection of the CO(3--2) line in the 3-mm window was confirmed via observations of CO(5--4) in the 2-mm window Both lines constrain the redshift of SMMJ14009+0252 to z=29344, with high precision (dz=2 10^{-4}) Such observations will become routine in determining redshifts in the era of the Atacama Large Millimeter/submillimeter Array (ALMA)

First redshift determination of an optically/ultraviolet faint submillimeter galaxy using co emission lines

Abstract: We report the redshift of a distant, highly obscured submillimeter galaxy (SMG), based entirely on the detection of its CO line emission. We have used the newly commissioned Eight MIxer Receiver at the IRAM 30 m telescope, with its 8 GHz of instantaneous dual-polarization bandwidth, to search the 3 mm atmospheric window for CO emission from SMM J14009+0252, a bright SMG detected in SCUBA Lens Survey. A detection of the CO(3-2) line in the 3 mm window was confirmed via observations of CO(5-4) in the 2 mm window. Both lines constrain the redshift of SMM J14009+0252 to z = 2.9344, with high precision (deltaz = 2 x 10{sup -4}). Such observations will become routine in determining redshifts in the era of ALMA.

SPACE: the spectroscopic all-sky cosmic explorer

Abstract: We describe the scientific motivations, the mission concept and the instrumentation of SPACE, a class-M mission proposed for concept study at the first call of the ESA Cosmic-Vision 2015–2025 planning cycle. SPACE aims to produce the largest three-dimensional evolutionary map of the Universe over the past 10 billion years by taking near-IR spectra and measuring redshifts for more than half a billion galaxies at 0 < z < 2 down to AB~23 over 3π sr of the sky. In addition, SPACE will also target a smaller sky field, performing a deep spectroscopic survey of millions of galaxies to AB~26 and at 2 < z < 10 +. These goals are unreachable with ground-based observations due to the ≈500 times higher sky background (see e.g. Aldering, LBNL report number LBNL-51157, 2001). To achieve the main science objectives, SPACE will use a 1.5 m diameter Ritchey-Chretien telescope equipped with a set of arrays of Digital Micro-mirror Devices covering a total field of view of 0.4 deg2, and will perform large-multiplexing multi-object spectroscopy (e.g. ≈6000 targets per pointing) at a spectral resolution of R~400 as well as diffraction-limited imaging with continuous coverage from 0.8 to 1.8 μm. Owing to the depth, redshift range, volume coverage and quality of its spectra, SPACE will reveal with unique sensitivity most of the fundamental cosmological signatures, including the power spectrum of density fluctuations and its turnover. SPACE will also place high accuracy constraints on the dark energy equation of state parameter and its evolution by measuring the baryonic acoustic oscillations imprinted when matter and radiation decoupled, the distance-luminosity relation of cosmological supernovae, the evolution of the cosmic expansion rate, the growth rate of cosmic large-scale structure, and high-z galaxy clusters. The datasets from the SPACE mission will represent a long lasting legacy for the whole astronomical community whose data will be mined for many years to come.

NEAR-INFRARED SPECTROSCOPY OF SDSS J0303 – 0019: A LOW-LUMINOSITY, HIGH-EDDINGTON-RATIO QUASAR AT z ∼ 6

Abstract: We present sensitive near-infrared (NIR) VLT ISAAC spectroscopic observations of the z = 6.08 quasar SDSS J030331.40-001912.9. This quasi-stellar object (QSO) is more than a magnitude fainter than other QSOs at z ~ 6 for which NIR spectroscopy has been obtained to date and is therefore presumably more representative of the QSO population at the end of cosmic reionization. Combining rest-frame UV continuum luminosity with the width measurements of the Mg II and C IV lines, we derive a black hole mass of 2+1.0 –0.5 × 108 M ☉, the lowest mass observed for z ~ 6 QSOs to date, and derive an Eddington ratio of 1.6+0.4 –0.6, among the highest value derived for QSOs at any redshift. The Spitzer 24 μm nondetection of this QSO does not leave space for a significant hot dust component in its optical/NIR spectral energy distribution, in common with one other faint QSO at z = 6, but in contrast to more than 20 more z = 6 QSOs and all known lower redshift QSOs with sufficiently deep multiwavelength photometry. We conclude that we have found evidence for differences in the intrinsic properties of at least one z ~ 6 QSO as compared to the lower redshift population.

NIR spectroscopy of SDSS J0303-0019: a low luminosity, high Eddington ratio quasar at z~6

Abstract: We present sensitive near--infrared VLT ISAAC spectroscopic observations of the z=6.08 quasar SDSS J030331.40-001912.9. This QSO is more than a magnitude fainter than other QSOs at z~6 for which NIR spectroscopy has been obtained to date and is therefore presumably more representative of the QSO population at the end of Cosmic Reionization. Combining rest--frame UV continuum luminosity with the width measurements of the Mg II and C IV lines, we derive a black hole mass of 2(+1.0/-0.5) x 10^8 solar masses, the lowest mass observed for z~6 QSOs to date, and derive an Eddington ratio of 1.6(+0.4/-0.6), amongst the highest value derived for QSOs at any redshift. The Spitzer 24 micron non--detection of this QSO does not leave space for a significant hot dust component in its optical/near--infrared SED, in common with one other faint QSO at z=6, but in contrast to more than twenty more z=6 QSOs and all known lower redshift QSOs with sufficiently deep multi-wavelength photometry. We conclude that we have found evidence for differences in the intrinsic properties of at least one z~6 QSO as compared to the lower--redshift population.

Does Stellar Feedback Create H I Holes? A Hubble Space Telescope/Very Large Array Study of Holmberg II

Abstract: We use deep Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) F555W and F814W photometry of resolved stars in the M81 Group dwarf irregular galaxy Ho II to study the hypothesis that the holes identified in the neutral interstellar medium (H I) are created by stellar feedback. From the deep photometry, we construct color-magnitude diagrams (CMDs) and measure the star formation histories (SFHs) for stars contained in H I holes from two independent holes catalogs, as well as select control fields, i.e., similar sized regions that span a range of H I column densities. The CMDs reveal young (< 200 Myr) stellar populations inside all H I holes, which contain very few bright OB stars with ages less than 10 Myr, indicating they are not reliable tracers of H I hole locations while the recent SFHs confirm multiple episodes of star formation within most holes. Converting the recent SFHs into stellar feedback energies, we find that enough energy has been generated to have created all holes. However, the required energy is not always produced over a timescale that is less than the estimated kinematic age of the hole. A similar analysis of stars in the control fields finds that the stellar populations of the control fields and H I holes are statistically indistinguishable. However, because we are only sensitive to holes ~100 pc in diameter, we cannot tell if there are smaller holes inside the control fields. The combination of the CMDs, recent SFHs, and locations of young stars shows that the stellar populations inside H I holes are not coherent, single-aged, stellar clusters, as previously suggested, but rather multi-age populations distributed across each hole. From a comparison of the modeled and observed integrated magnitudes, and the locations and energetics of stars inside of H I holes, we propose a potential new model: a viable mechanism for creating the observed H I holes in Ho II is stellar feedback from multiple generations of SF spread out over tens or hundreds of Myr, and thus, the concept of an age for an H I hole is intrinsically ambiguous. For H I holes in the outer parts of Ho II, located beyond the HST/ACS coverage, we use Monte Carlo simulations of expected stellar populations to show that low level SF could provide the energy necessary to form these holes. Applying the same method to the SMC, we find that the holes that appear to be void of stars could have formed via stellar feedback from low level SF. We further find that Hα and 24 μm emission, tracers of the most recent star formation, do not correlate well with the positions of the H I holes. However, UV emission, which traces star formation over roughly the last 100 Myr, shows a much better correlation with the locations of the H I holes.

CO line emission in the halo of a radio galaxy at z = 2.6

Abstract: We report the detection of luminous CO(3-2) line emission in the halo of the z = 2.6 radio galaxy (HzRG) TXS0828+193, which has no detected counterpart at optical to mid-infrared wavelengths implying a stellar mass less than or similar to few x 10(9) M-circle dot and relatively low star formation rates. With the IRAM Plateau de Bure Interferometer (PdBI), we find two CO emission-line components at the same position at similar to 80 kpc distance from the HzRG along the axis of the radio jet, with different blueshifts of few 100 km s(-1) relative to the HzRG and a total luminosity of similar to 2 x 10(10) K km s(-1) pc(2) detected at a total significance of similar to 8 sigma. HzRGs have significant galaxy overdensities and extended haloes of metal-enriched gas often with embedded clouds or filaments of denser material, and likely trace very massive dark matter haloes. The CO emission may be associated with a gas-rich, low-mass satellite galaxy with very little ongoing star formation, in contrast to all previous CO detections of galaxies at similar redshifts. Alternatively, the CO may be related to a gas cloud or filament and perhaps jet-induced gas cooling in the outer halo, somewhat in analogy with extended CO emission found in low-redshift galaxy clusters.

Does Stellar Feedback Create HI Holes? An HST/VLA Study of Holmberg II

Abstract: We use deep HST/ACS F555W and F814W photometry of resolved stars in the M81 Group dwarf irregular galaxy Ho II to study the hypothesis that the holes identified in the neutral ISM (HI) are created by stellar feedback. From the deep photometry, we construct color-magnitude diagrams (CMDs) and measure the star formation histories (SFHs) for stars contained in HI holes from two independent holes catalogs, as well as select control fields, i.e., similar sized regions that span a range of HI column densities. Converting the recent SFHs into stellar feedback energies, we find that enough energy has been generated to have created all holes. However, the required energy is not always produced over a time scale that is less than the estimated kinematic age of the hole. The combination of the CMDs, recent SFHs, and locations of young stars shows that the stellar populations inside HI holes are not coherent, single-aged, stellar clusters, as previously suggested, but rather multi-age populations distributed across each hole. From a comparison of the modeled and observed integrated magnitudes, and the locations and energetics of stars inside of HI holes, we propose a potential new model: a viable mechanism for creating the observed HI holes in Ho II is stellar feedback from multiple generations of SF spread out over tens or hundreds of Myr, and thus, the concept of an age for an HI hole is intrinsically ambiguous. We further find that \halpha and 24 micron emission, tracers of the most recent star formation, do not correlate well with the positions of the HI holes. However, UV emission, which traces star formation over roughly the last 100 Myr, shows a much better correlation with the locations of the HI holes.

Very High Gas Fractions and Extended Gas Reservoirs in z=1.5 Disk Galaxies

Abstract: We present evidence for very high gas fractions and extended molecular gas reservoirs in normal, near-infrared selected (BzK) galaxies at z~1.5, based on multi-configuration CO[2-1] observations obtained at the IRAM PdBI. Six of the six galaxies observed were securely detected. High resolution observations resolve the CO emission in four of them, implying sizes of order of 6-11 kpc and suggesting the presence of rotation. The UV morphologies are consistent with clumpy, unstable disks, and the UV sizes are consistent with the CO sizes. The star formation efficiencies are homogeneously low and similar to local spirals - the resulting gas depletion times are ~0.5 Gyr, much higher than what is seen in high-z submm galaxies and quasars. The CO luminosities can be predicted to within 0.15 dex from the star formation rates and stellar masses, implying a tight correlation of the gas mass with these quantities. We use dynamical models of clumpy disk galaxies to derive dynamical masses. These models are able to reproduce the peculiar spectral line shapes of the CO emission. After accounting for the stellar and dark matter masses we derive gas masses of 0.4-1.2x10^11 Msun. The conversion factor is very high: alpha_CO=3.6+-0.8, consistent with the Galaxy but four times higher than that of local ultra-luminous IR galaxies. The gas accounts for an impressive 50-65% of the baryons within the galaxies' half light radii. We are witnessing truly gas-dominated galaxies at z~1.5, a finding that explains the high specific SFRs observed for z>1 galaxies. The BzK galaxies can be viewed as scaled-up versions of local disk galaxies, with low efficiency star formation taking place inside extended, low excitation gas disks. They are markedly different than local ULIRGs and high-z submm galaxies, which have more excited and compact gas.

A LABOCA survey of the Extended Chandra Deep Field South - submillimeter properties of near-IR selected galaxies

Abstract: Using the 330hr ESO-MPG 870-micron survey of the Extended Chandra Deep Field South (ECDF-S) obtained with the Large Apex BOlometer CAmera (LABOCA) on the Atacama Pathfinder EXperiment (APEX), we have carried out a stacking analysis at submillimeter (submm) wavelengths of a sample of 8266 near-infra-red (near-IR) selected (K_vega <= 20) galaxies, including 893 BzK galaxies, 1253 extremely red objects (EROs) and 737 distant red galaxies (DRGs), selected from the Multi-wavelength Survey by Yale-Chile (MUSYC). We measure average 870-micron fluxes of 0.20+-0.01mJy (20.0sigma), 0.45+-0.04mJy (11.3sigma), 0.42+-0.03mJy (14.0sigma), and 0.41+-0.04mJy (10.3sigma) for the K_vega <= 20, BzK, ERO and DRG samples, respectively. For the BzK, ERO and DRG subsamples, which overlap to some degree and are like to be at z ~ 1-2, this implies an average far-IR luminosity of ~2-6x10^{11} Lsolar and star formation rate of ~40-100Msolar. Splitting the BzK galaxies up into star-forming (sBzK) and passive (pBzK) galaxies, the former is significantly detected (0.48+-0.04mJy, 12.0sigma) while the latter is only marginally detected (0.27+-0.10mJy, 2.7sigma), thus confirming that the sBzK/pBzK criteria do isolate obscured, star forming and truly passive galaxies. The K_vega <= 20 galaxies are found to contribute with 6.6+-0.3Jy deg^{-2} (~15%) to the 870-micron extragalactic background light (EBL). sBzK and pBzK galaxies contribute 1.7+-0.2Jy deg^{-2} (~4%) and 0.2+-0.1 Jy deg^{-2} (< 0.5%) to the EBL. [Abridged]

Triggered Star Formation and the Creation of the Supergiant H I Shell in IC 2574

Abstract: Based on deep imaging from the Advanced Camera for Surveys aboard the Hubble Space Telescope (HST), we present new evidence that stellar feedback created a ~1 kpc supergiant H I 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 H I and SF, we find compelling evidence that stellar feedback is responsible for creating the SGS and triggering secondary SF around its rim

The Spitzer Local Volume Legacy: Survey Description and Infrared Photometry

Abstract: The survey description and the near-, mid-, and far-infrared flux properties are presented for the 258 galaxies in the Local Volume Legacy (LVL). LVL is a Spitzer Space Telescope legacy program that surveys the local universe out to 11 Mpc, built upon a foundation of ultraviolet, H-alpha, and HST imaging from 11HUGS (11 Mpc H-alpha and Ultraviolet Galaxy Survey) and ANGST (ACS Nearby Galaxy Survey Treasury). LVL covers an unbiased, representative, and statistically robust sample of nearby star-forming galaxies, exploiting the highest extragalactic spatial resolution achievable with Spitzer. As a result of its approximately volume-limited nature, LVL augments previous Spitzer observations of present-day galaxies with improved sampling of the low-luminosity galaxy population. The collection of LVL galaxies shows a large spread in mid-infrared colors, likely due to the conspicuous deficiency of 8um PAH emission from low-metallicity, low-luminosity galaxies. Conversely, the far-infrared emission tightly tracks the total infrared emission, with a dispersion in their flux ratio of only 0.1 dex. In terms of the relation between infrared-to-ultraviolet ratio and ultraviolet spectral slope, the LVL sample shows redder colors and/or lower infrared-to-ultraviolet ratios than starburst galaxies, suggesting that reprocessing by dust is less important in the lower mass systems that dominate the LVL sample. Comparisons with theoretical models suggest that the amplitude of deviations from the relation found for starburst galaxies correlates with the age of the stellar populations that dominate the ultraviolet/optical luminosities.