20 research outputs found
A New Star-Formation Rate Calibration from Polycyclic Aromatic Hydrocarbon Emission Features and Application to High Redshift Galaxies
We calibrate the integrated luminosity from the polycyclic aromatic
hydrocarbon (PAH) features at 6.2\micron, 7.7\micron\ and 11.3\micron\ in
galaxies as a measure of the star-formation rate (SFR). These features are
strong (containing as much as 5-10\% of the total infrared luminosity) and
suffer minimal extinction. Our calibration uses \spitzer\ Infrared Spectrograph
(IRS) measurements of 105 galaxies at , infrared (IR) luminosities
of 10^9 - 10^{12} \lsol, combined with other well-calibrated SFR indicators.
The PAH luminosity correlates linearly with the SFR as measured by the
extinction-corrected \ha\ luminosity over the range of luminosities in our
calibration sample. The scatter is 0.14 dex comparable to that between SFRs
derived from the \paa\ and extinction-corrected \ha\ emission lines, implying
the PAH features may be as accurate a SFR indicator as hydrogen recombination
lines. The PAH SFR relation depends on gas-phase metallicity, for which we
supply an empirical correction for galaxies with 0.2 < \mathrm{Z} \lsim
0.7~\zsol. We present a case study in advance of the \textit{James Webb Space
Telescope} (\jwst), which will be capable of measuring SFRs from PAHs in
distant galaxies at the peak of the SFR density in the universe () with
SFRs as low as ~10~\sfrunits. We use \spitzer/IRS observations of the PAH
features and \paa\ emission plus \ha\ measurements in lensed star-forming
galaxies at to demonstrate the ability of the PAHs to derive
accurate SFRs. We also demonstrate that because the PAH features dominate the
mid-IR fluxes, broad-band mid-IR photometric measurements from \jwst\ will
trace both the SFR and provide a way to exclude galaxies dominated by an AGN.Comment: Accepted for publication in Ap
Spitzer Spectroscopy of Infrared-Luminous Galaxies: Diagnostics of AGN and Star Formation and Contribution to Total Infrared Luminosity
We use Spitzer IRS spectroscopy to study the nature 65 IR-luminous galaxies
at 0.02 1.2mJy. The IRS spectra cover wavelengths
spanning the PAH features and important atomic diagnostic lines. Our sample
corresponds to L(IR) = L(8-1000micron) = 10^10-10^12 Lsun. We divide our
galaxies into those with Spitzer IRAC colors indicative of warm dust heated by
an AGN (IRAGN) and those whose colors indicate star-formation processes
(non-IRAGN). Compared to the non-IRAGN, the IRAGN show smaller PAH emission
EWs, which we attribute to an increase in mid-IR continuum from the AGN. We
find that in both the IRAGN and non-IRAGN samples, the PAH luminosities
correlate strongly with the [Ne II] emission, from which we conclude that the
PAH luminosity directly traces the instantaneous SFR in both the IRAGN and
non-IRAGN galaxies. We compare the ratio of PAH luminosity to the total IR
luminosity and show that for most IRAGN star-formation accounts for 10-50% of
the L(IR). We also find no measurable difference between the PAH luminosity
ratios of L(11.3)/L(7.7) and L(6.2)/L(7.7) for the IRAGN and non-IRAGN,
suggesting that AGN do not significantly excite or destroy PAH molecules on
galaxy-wide scales. A small subset of galaxies show excess of [O IV] emission
compared to their PAH emission, which indicates the presence of
heavily-obscured AGN, including 3 galaxies that are not otherwise selected as
IRAGN. The low PAH emission and low [Ne II] emission of the IRAGN and [O
IV]-excess objects imply they have low SFRs and their IR luminosity is
dominated by processes associated with the AGN.Comment: 22 pages, 18 figures, accepted for publication in Ap
HFF-DeepSpace photometric catalogs of the 12 Hubble frontier fields, clusters, and parallels : photometry, photometric redshifts, and stellar masses
We present Hubble multi-wavelength photometric catalogs, including (up to) 17 filters with the Advanced Camera for Surveys and Wide Field Camera 3 from the ultra-violet to near-infrared for the Hubble Frontier Fields and associated parallels. We have constructed homogeneous photometric catalogs for all six clusters and their parallels. To further expand these data catalogs, we have added ultra-deep KS-band imaging at 2.2. mu m from the Very Large Telescope HAWK-I and Keck-I MOSFIRE instruments. We also add post-cryogenic Spitzer imaging at 3.6 and 4.5. mu m with the Infrared Array Camera (IRAC), as well as archival IRAC 5.8 and 8.0. mu m imaging when available. We introduce the public release of the multi-wavelength (0.2-8 mu m) photometric catalogs, and we describe the unique steps applied for the construction of these catalogs. Particular emphasis is given to the source detection band, the contamination of light from the bright cluster galaxies (bCGs), and intra-cluster light (ICL). In addition to the photometric catalogs, we provide catalogs of photometric redshifts and stellar population properties. Furthermore, this includes all the images used in the construction of the catalogs, including the combined models of bCGs and ICL, the residual images, segmentation maps, and more. These catalogs are a robust data set of the Hubble Frontier Fields and will be an important aid in designing future surveys, as well as planning follow-up programs with current and future observatories to answer key questions remaining about first light, reionization, the assembly of galaxies, and many more topics, most notably by identifying high-redshift sources to target
Resolved stellar mass maps of galaxies in the Hubble Frontier Fields : evidence for mass dependency in environmental quenching
One of the challenges in understanding the quenching processes for galaxies is connecting progenitor star-forming populations to their descendant quiescent populations over cosmic time. Here we attempt a novel approach to this challenge by assuming that the underlying stellar mass distribution of galaxies is not significantly altered during environmental-quenching processes that solely affect the gas content of cluster galaxies, such as strangulation and ram pressure stripping. Using the deep, high-resolution photometry of the Hubble Frontier Fields, we create resolved stellar mass maps for both cluster and field galaxies, from which we determine 2D Sersic profiles, and obtain Sersic indices and half-mass radii. We classify the quiescent cluster galaxies into disk-like and bulge-like populations based on their Sersic indices, and find that bulge-like quiescent galaxies dominate the quiescent population at higher masses (M-star > 10(9.5)M(circle dot)), whereas disk-like quiescent galaxies dominate at lower masses (10(8.5)M(circle dot) < M-star < 10(9.5)M(circle dot)). Using both the Sersic indices and half-mass radii, we identify a population of quiescent galaxies in clusters that are morphological analogs of field star-forming galaxies. These analogs are interpreted to be star-forming galaxies that had been environmentally quenched. We use these morphological analogs to compute the environmental-quenching efficiency, and we find that the efficiency decreases with increasing stellar mass. This demonstrates that environmental quenching is more effective on less massive galaxies and that the effect of environment on quenching galaxies is not completely separable from the effect of mass on quenching galaxies
Extending the evolution of the stellar massâsize relation at z †2 to low stellar mass galaxies from HFF and CANDELS
30 pages, 19 figures, Accepted for publication in MNRASInternational audienceWe reliably extend the stellar massâsize relation over 0.2 †z †2 to low stellar mass galaxies by combining the depth of Hubble Frontier Fields with the large volume covered by CANDELS. Galaxies are simultaneously modelled in multiple bands using the tools developed by the MegaMorph project, allowing robust size (i.e. half-light radius) estimates even for small, faint, and high redshift galaxies. We show that above 107 Mâ, star-forming galaxies are well represented by a single power law on the massâsize plane over our entire redshift range. Conversely, the stellar massâsize relation is steep for quiescent galaxies with stellar masses and flattens at lower masses, regardless of whether quiescence is selected based on star-formation activity, rest-frame colours, or structural characteristics. This flattening occurs at sizes of âŒ1 kpc at z †1. As a result, a double power law is preferred for the stellar massâsize relation of quiescent galaxies, at least above 10. We find no strong redshift dependence in the slope of the relation of star-forming galaxies as well as of high mass quiescent galaxies. We also show that star-forming galaxies with stellar masses and quiescent galaxies with stellar masses have undergone significant size growth since z ⌠2, as expected; however, low mass galaxies have not. Finally, we supplement our data with predominantly quiescent dwarf galaxies from the core of the Fornax cluster, showing that the stellar massâsize relation is continuous below 10, but a more complicated functional form is necessary to describe the relation