Showing papers by "Deidre A. Hunter published in 2016"
TL;DR: In this paper, the authors determined new relations between UBV colors and mass-to-light ratios (M/L) for dwarf irregular (dIrr) galaxies, as well as for transformed g' − r'.
Abstract: We have determined new relations between UBV colors and mass-to-light ratios (M/L) for dwarf irregular (dIrr) galaxies, as well as for transformed g' − r'. These M/L to color relations (MLCRs) are based on stellar mass density profiles determined for 34 LITTLE THINGS dwarfs from spectral energy distribution fitting to multi-wavelength surface photometry in passbands from the FUV to the NIR. These relations can be used to determine stellar masses in dIrr galaxies for situations where other determinations of stellar mass are not possible. Our MLCRs are shallower than comparable MLCRs in the literature determined for spiral galaxies. We divided our dwarf data into four metallicity bins and found indications of a steepening of the MLCR with increased oxygen abundance, perhaps due to more line blanketing occurring at higher metallicity.
34 citations
TL;DR: In this paper, far-infrared (FIR) spectral line observations of five galaxies from the Little Things sample: DDO 69, DDO 70, D DO 75, D DOE 155, and WLM were used to study the properties of these systems on the scales of larger star-forming complexes.
Abstract: We present far-infrared (FIR) spectral line observations of five galaxies from the Little Things sample: DDO 69, DDO 70, DDO 75, DDO 155, and WLM. While most studies of dwarfs focus on bright systems or starbursts due to observational constraints, our data extend the observed parameter space into the regime of low surface brightness dwarf galaxies with low metallicities and moderate star formation rates. Our targets were observed with Herschel at the [C ii] 158 μm, [O i] 63 μm, [O iii] 88 μm, and [N ii] 122 μm emission lines using the PACS Spectrometer. These high-resolution maps allow us for the first time to study the FIR properties of these systems on the scales of larger star-forming complexes. The spatial resolution in our maps, in combination with star formation tracers, allows us to identify separate photodissociation regions (PDRs) in some of the regions we observed. Our systems have widespread [C ii] emission that is bright relative to continuum, averaging near 0.5% of the total infrared (TIR) budget—higher than in solar-metallicity galaxies of other types. [N ii] is weak, suggesting that the [C ii] emission in our galaxies comes mostly from PDRs instead of the diffuse ionized interstellar medium (ISM). These systems exhibit efficient cooling at low dust temperatures, as shown by ([O i]+[C ii])/TIR in relation to 60 μm/100 μm, and low [O i]/[C ii] ratios which indicate that [C ii] is the dominant coolant of the ISM. We observe [O iii]/[C ii] ratios in our galaxies that are lower than those published for other dwarfs, but similar to levels noted in spirals.
33 citations
TL;DR: In this article, the B-V, U-B, and FUV-NUV radial color trends from a multi-wavelength sample of 141 dwarf disk galaxies were explored.
Abstract: In this second paper of a series, we explore the B-V, U-B, and FUV-NUV radial color trends from a multi-wavelength sample of 141 dwarf disk galaxies. Like spirals, dwarf galaxies have three types of radial surface brightness profiles: (I) single exponential throughout the observed extent (the minority), (II) down-bending (the majority), and (III) up-bending. We find that colors of (1) Type I dwarfs generally become redder with increasing radius unlike spirals that have a blueing trend that flattens beyond ~1.5 disk scale lengths, (2) Type II dwarfs come in six different "flavors," one of which mimics the "U" shape of spirals, and (3) Type III dwarfs have a stretched "S" shape where central colors are flattish, become steeply redder to the surface brightness break, then remain roughly constant beyond, similar to spiral TypeIII color profiles, but without the central outward bluing. Faint (-9 > M_B > -14) Type II dwarfs tend to have continuously red or "U" shaped colors and steeper color slopes than bright (-14 > M_B > -19) Type II dwarfs, which additionally have colors that become bluer or remain constant with increasing radius. Sm dwarfs and BCDs tend to have at least some blue and red radial color trend, respectively. Additionally, we determine stellar surface mass density (Sigma) profiles and use them to show that the break in Sigma generally remains in Type II dwarfs (unlike Type II spirals) but generally disappears in Type III dwarfs (unlike Type III spirals). Moreover, the break in Sigma is strong, intermediate, and weak in faint dwarfs, bright dwarfs, and spirals, respectively, indicating that Sigma may straighten with increasing galaxy mass. Lastly, the average stellar surface mass density at the surface brightness break is roughly 1-2 M_S/pc^2 for Type II dwarfs but higher at 5.9 M_S/pc^2 or 27 M_S/pc^2 for Type III BCDs and dIms, respectively.
21 citations
TL;DR: In this article, the B-V, U-B, and FUV-NUV radial color trends from a multi-wavelength sample of 141 dwarf disk galaxies were explored.
Abstract: In this second paper of a series, we explore the B-V, U-B, and FUV-NUV radial color trends from a multi-wavelength sample of 141 dwarf disk galaxies. Like spirals, dwarf galaxies have three types of radial surface brightness profiles: (I) single exponential throughout the observed extent (the minority), (II) down-bending (the majority), and (III) up-bending. We find that colors of (1) Type I dwarfs generally become redder with increasing radius unlike spirals that have a blueing trend that flattens beyond ~1.5 disk scale lengths, (2) Type II dwarfs come in six different "flavors," one of which mimics the "U" shape of spirals, and (3) Type III dwarfs have a stretched "S" shape where central colors are flattish, become steeply redder to the surface brightness break, then remain roughly constant beyond, similar to spiral TypeIII color profiles, but without the central outward bluing. Faint (-9 > M_B > -14) Type II dwarfs tend to have continuously red or "U" shaped colors and steeper color slopes than bright (-14 > M_B > -19) Type II dwarfs, which additionally have colors that become bluer or remain constant with increasing radius. Sm dwarfs and BCDs tend to have at least some blue and red radial color trend, respectively. Additionally, we determine stellar surface mass density (Sigma) profiles and use them to show that the break in Sigma generally remains in Type II dwarfs (unlike Type II spirals) but generally disappears in Type III dwarfs (unlike Type III spirals). Moreover, the break in Sigma is strong, intermediate, and weak in faint dwarfs, bright dwarfs, and spirals, respectively, indicating that Sigma may straighten with increasing galaxy mass. Lastly, the average stellar surface mass density at the surface brightness break is roughly 1-2 M_S/pc^2 for Type II dwarfs but higher at 5.9 M_S/pc^2 or 27 M_S/pc^2 for Type III BCDs and dIms, respectively.
6 citations
TL;DR: In this article, the authors determined new relations between $UBV$ colors and mass-to-light ratios (M/L$) for dwarf irregular (dIrr) galaxies, as well as for transformed $g^\ prime - r^\prime.
Abstract: We have determined new relations between $UBV$ colors and mass-to-light ratios ($M/L$) for dwarf irregular (dIrr) galaxies, as well as for transformed $g^\prime - r^\prime$. These $M/L$ to color relations (MLCRs) are based on stellar mass density profiles determined for 34 LITTLE THINGS dwarfs from spectral energy distribution fitting to multi-wavelength surface photometry in passbands from the FUV to the NIR. These relations can be used to determine stellar masses in dIrr galaxies for situations where other determinations of stellar mass are not possible. Our MLCRs are shallower than comparable MLCRs in the literature determined for spiral galaxies. We divided our dwarf data into four metallicity bins and found indications of a steepening of the MLCR with increased oxygen abundance, perhaps due to more line blanketing occurring at higher metallicity.
5 citations
01 Mar 2016
TL;DR: In this paper, high-resolution observations with ALMA of CO clouds in the local group dwarf irregular galaxy WLM have been reported, which has a metallicity that is 13% of the solar value and 50% lower than the previous CO detection threshold.
Abstract: Understanding stellar birth requires observations of the clouds in which they form. These clouds are dense and self-gravitating, and in all existing observations, they are molecular with H2 the dominant species and CO the best available. When the abundances of carbon and oxygen are low compared to hydrogen, and the opacity from dust is also low, as in primeval galaxies and local dwarf irregular galaxies CO forms slowly and is easily destroyed, so it cannot accumulate inside dense clouds. Then we lose our ability to trace the gas in regions of star formation and we lose critical information on the temperatures, densities, and velocities of the material that collapses. I will report on high resolution observations with ALMA of CO clouds in the local group dwarf irregular galaxy WLM, which has a metallicity that is 13% of the solar value and 50% lower than the previous CO detection threshold and the properties derived of very small dense CO clouds mapped..