429 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
The [O II] lambda 3727 Luminosity Function at z ~ 1
We measure the evolution of the [OII]lambda 3727 luminosity function at
0.75<z<1.45 using high-resolution spectroscopy of ~14,000 galaxies observed by
the DEEP2 galaxy redshift survey. We find that brighter than L_{OII}=10^{42}
erg s^(-1) the luminosity function is well-represented by a power law dN/dL ~
L^{\alpha} with slope \alpha ~ -3. The number density of [OII] emitting
galaxies above this luminosity declines by a factor of >~2.5 between z ~ 1.35
and z ~ 0.84. In the limit of no number-density evolution, the characteristic
[OII] luminosity, L^*_[OII], defined as the luminosity where the space density
equals 10^{-3.5} dex^{-1} Mpc^{-3}, declines by a factor of ~1.8 over the same
redshift interval. Assuming that L_[OII] is proportional to the star-formation
rate (SFR), and negligible change in the typical dust attenuation in galaxies
at fixed [OII] luminosity, the measured decline in L^*_[OII] implies a ~25% per
Gyr decrease in the amount of star formation in galaxies during this epoch.
Adopting a faint-end power-law slope of -1.3\pm0.2, we derive the comoving SFR
density in four redshift bins centered around z~1 by integrating the observed
[OII] luminosity function using a local, empirical calibration between L_[OII]
and SFR, which statistically accounts for variations in dust attenuation and
metallicity among galaxies. We find that our estimate of the SFR density at z~1
is consistent with previous measurements based on a variety of independent SFR
indicators.Comment: 10 pages, 6 figures, 2 tables, resubmitted to ApJ, in emulateapj
style. Comparison with narrow-band observations added. Wavelength coverage
included into complete function, little effects. The data is available on
http://bias.cosmo.fas.nyu.edu/galevolution
PRIMUS: The relationship between Star formation and AGN accretion
We study the evidence for a connection between active galactic nuclei (AGN)
fueling and star formation by investigating the relationship between the X-ray
luminosities of AGN and the star formation rates (SFRs) of their host galaxies.
We identify a sample of 309 AGN with erg
s at in the PRIMUS redshift survey. We find AGN in
galaxies with a wide range of SFR at a given . We do not find a
significant correlation between SFR and the observed instantaneous for
star forming AGN host galaxies. However, there is a weak but significant
correlation between the mean and SFR of detected AGN in star
forming galaxies, which likely reflects that varies on shorter
timescales than SFR. We find no correlation between stellar mass and
within the AGN population. Within both populations of star
forming and quiescent galaxies, we find a similar power-law distribution in the
probability of hosting an AGN as a function of specific accretion rate.
Furthermore, at a given stellar mass, we find a star forming galaxy
more likely than a quiescent galaxy to host an AGN of a given specific
accretion rate. The probability of a galaxy hosting an AGN is constant across
the main sequence of star formation. These results indicate that there is an
underlying connection between star formation and the presence of AGN, but AGN
are often hosted by quiescent galaxies
A UV to Mid-IR Study of AGN Selection
We classify the spectral energy distributions (SEDs) of 431,038 sources in
the 9 sq. deg Bootes field of the NOAO Deep Wide-Field Survey (NDWFS). There
are up to 17 bands of data available per source, including ultraviolet (GALEX),
optical (NDWFS), near-IR (NEWFIRM), and mid-infrared (IRAC/MIPS) data, as well
as spectroscopic redshifts for ~20,000 objects, primarily from the AGN and
Galaxy Evolution Survey (AGES). We fit galaxy, AGN, stellar, and brown dwarf
templates to the observed SEDs, which yield spectral classes for the Galactic
sources and photometric redshifts and galaxy/AGN luminosities for the
extragalactic sources. The photometric redshift precision of the galaxy and AGN
samples are sigma/(1+z)=0.040 and sigma/(1+z)=0.169, respectively, with the
worst 5% outliers excluded. Based on the reduced chi-squared of the SED fit for
each SED model, we are able to distinguish between Galactic and extragalactic
sources for sources brighter than I=23.5. We compare the SED fits for a
galaxy-only model and a galaxy+AGN model. Using known X-ray and spectroscopic
AGN samples, we confirm that SED fitting can be successfully used as a method
to identify large populations of AGN, including spatially resolved AGN with
significant contributions from the host galaxy and objects with the emission
line ratios of "composite" spectra. We also use our results to compare to the
X-ray, mid-IR, optical color and emission line ratio selection techniques. For
an F-ratio threshold of F>10 we find 16,266 AGN candidates brighter than I=23.5
and a surface density of ~1900 AGN per deg^2.Comment: Submitted to ApJ, 35 pages, 17 figures, 2 table
PRIMUS: The Effect of Physical Scale on the Luminosity-Dependence of Galaxy Clustering via Cross-Correlations
We report small-scale clustering measurements from the PRIMUS spectroscopic
redshift survey as a function of color and luminosity. We measure the
real-space cross-correlations between 62,106 primary galaxies with PRIMUS
redshifts and a tracer population of 545,000 photometric galaxies over
redshifts from z=0.2 to z=1. We separately fit a power-law model in redshift
and luminosity to each of three independent color-selected samples of galaxies.
We report clustering amplitudes at fiducial values of z=0.5 and L=1.5 L*. The
clustering of the red galaxies is ~3 times as strong as that of the blue
galaxies and ~1.5 as strong as that of the green galaxies. We also find that
the luminosity dependence of the clustering is strongly dependent on physical
scale, with greater luminosity dependence being found between r=0.0625 Mpc/h
and r=0.25 Mpc/h, compared to the r=0.5 Mpc/h to r=2 Mpc/h range. Moreover,
over a range of two orders of magnitude in luminosity, a single power-law fit
to the luminosity dependence is not sufficient to explain the increase in
clustering at both the bright and faint ends at the smaller scales. We argue
that luminosity-dependent clustering at small scales is a necessary component
of galaxy-halo occupation models for blue, star-forming galaxies as well as for
red, quenched galaxies.Comment: 13 pages, 6 figures, 5 tables; published in ApJ (revised to match
published version
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