394 research outputs found
How many active galaxies and QSOs will future Space Missions detect?
Averaged spectral energy distributions (SEDs) of active and starburst
galaxies from the 12 micron sample in the Local Universe and Quasars, from an
optically selected sample at a mean redshift =0.7, are built from
optical/near-IR/far-IR (IRAS & ISO) photometric observations. These SEDs are
then used to predict at various redshifts the number of Seyfert type 1 and type
2, starburst, normal galaxies, and quasars, that will be detected by future
Space Missions dedicated to far-infrared and submillimeter astronomy, like
SIRTF and Herschel. These predictions are then compared with the expected
capabilities and detection limits of future deep far-IR surveys. Possible ways
to identify AGN candidates on far-IR colour-colour plots for follow-up
observations are then explored.Comment: accepted in Ap
DEIMOS Observations of WISE-Selected, Optically Obscured AGNs
While there are numerous criteria for photometrically identifying active
galactic nuclei (AGNs), searches in the optical and UV tend to exclude galaxies
that are highly dust obscured. This is problematic for constraining models of
AGN evolution and estimating the AGN contribution to the cosmic X-ray and IR
backgrounds, as highly obscured objects tend to be underrepresented in
large-scale surveys. To address this, we identify potentially obscured AGNs
using mid-IR color colors from the Wide-field Infrared Survey Explorer (WISE)
catalog. This paper presents the results of optical spectroscopy of obscured
AGN candidates using Keck DEIMOS, and their physical properties derived from
these spectra. We find that a color criterion effectively selects
AGNs with a higher median level of extinction compared to the AGNs
found in the SDSS DR7 survey. This optical extinction can be measured using SED
modeling or by using as a measure of optical to IR flux. We find that
specific, targeted observations are necessary to find the most highly optically
obscured AGNs, and that additional far-IR photometry is necessary to further
constrain the dust properties of these AGNs.Comment: 20 pages, 25 figures, accepted by MNRA
An Empirical Determination of the Intergalactic Background Light Using NIR Deep Galaxy Survey Data out to 5 microns and the Gamma-ray Opacity of the Universe
We extend our previous model-independent determination of the intergalactic
background light (IBL), based purely on galaxy survey data, out to a wavelength
of 5 microns. Our approach enables us to constrain the range of photon
densities, based on the uncertainties from observationally determined
luminosity densities and colors. We further determine a 68% confidence upper
and lower limit on the opacity of the universe to gamma-rays up to energies of
1.6/(1+z) TeV. A comparison of our lower limit redshift-dependent opacity
curves to the opacity limits derived from the results of both ground-based air
Cherenkov telescope and Fermi-LAT observations of PKS 1424+240 allows us to
place a new upper limit on the redshift of this source, independent of IBL
modeling.Comment: version accepted for publication in the Astrophysical Journal, 23
pages, 4 figure
The Bright Ages Survey. II. Evolution of Luminosity, Dust Extinction, and Star Formation from z = 0.5 to z = 2.5
The Bright Ages Survey is a K-band-selected redshift survey over six separate fields with UBVRIzJHK imaging covering a total of 75.6 arcmin(2) and reaching K = 20-20.5. Two fields have deep HST imaging, while all are centered on possible overdensities in the z similar to 2 range. Here we report photometric redshifts and spectroscopy for this sample, which has been described in Paper I. We find 18 galaxies with spectroscopic redshifts of z > 1:5. The derived rest-frame R-band luminosity functions show strong evolution out to z = 2. The luminosity function at z = 2 shows more bright galaxies than at any other epoch, even the extrapolated z = 3 luminosity function from Shapley et al. However, the R-band integrated luminosity density remains roughly constant from to z = 0:5 to z = 2. Evolved galaxies (E, S0, Sa) show a decreasing contribution to the total R-band luminosity density with redshift. The dust extinction in our K-selected sample is moderately larger [median z = 2 E(B - V) 0:30] than that found in Lyman break
galaxies, although not enough to make a significant impact on the total light or star formation found at high redshift. We measure the extinction-corrected star formation rate density at z 2, finding ρ_(SFR)(z = 1.5-2.5)= 0.093 M_⊙ yr^(-1) Mpc^(-3), consistent with a relatively flat instantaneous star formation rate from z = 1-4
The Metal Abundances across Cosmic Time () Survey. II. Evolution of the Mass-Metallicity Relation over 8 Billion Years, using [OIII]4363\AA-based Metallicities
We present the first results from MMT and Keck spectroscopy for a large
sample of emission-line galaxies selected from our narrow-band
imaging in the Subaru Deep Field. We measured the weak [OIII]4363
emission line for 164 galaxies (66 with at least 3 detections, and 98
with significant upper limits). The strength of this line is set by the
electron temperature for the ionized gas. Because the gas temperature is
regulated by the metal content, the gas-phase oxygen abundance is inversely
correlated with [OIII]4363 line strength. Our temperature-based
metallicity study is the first to span 8 Gyr of cosmic time and
3 dex in stellar mass for low-mass galaxies, . Using extensive multi-wavelength
photometry, we measure the evolution of the stellar mass--gas metallicity
relation and its dependence on dust-corrected star formation rate (SFR). The
latter is obtained from high signal-to-noise Balmer emission-line measurements.
Our mass-metallicity relation is consistent with Andrews & Martini at
, and evolves toward lower abundances at a given stellar mass,
. We find that galaxies
with lower metallicities have higher SFRs at a given stellar mass and redshift,
although the scatter is large (0.3 dex), and the trend is weaker than
seen in local studies. We also compare our mass--metallicity relation against
predictions from high-resolution galaxy formation simulations, and find good
agreement with models that adopt energy- and momentum-driven stellar feedback.
We have identified 16 extremely metal-poor galaxies with abundances less than a
tenth of solar; our most metal-poor galaxy at is similar to I Zw
18.Comment: 18 pages, 11 figures, 2 tables. Updated to match published version in
the Astrophysical Journa
Spitzer spectra of Seyfert galaxies
The Spitzer IRS high resolution spectra of about 90 Seyfert galaxies from the
12um Galaxy Sample are presented and discussed. These represent about 70% of
the total complete sample of local Seyfert galaxies. The presence of starburst
components in these galaxies can be quantified by powerful mid-IR diagnostics
tools (i.e. 11.25um PAH feature equivalent width and the H_2 emission line
intensity) as well as the AGN dominance can be measured by specific fine
structure line ratios (e.g. [NeV]/[NeII], [NeV]/[SiII], etc.). The observed
line ratios are compared to the results of semianalytical models, which can be
used to compute the AGN and starburst contributions to the total luminosity of
the galaxies. The results are also discussed in the light of unification and
evolution models.Comment: to appear in the proceedings of "The Starburst-AGN Connection
Conference", Shanghai, China, 27 Oct - 1 Nov 2008, ASP Conference Serie
Rest Frame Optical Spectra of Lyman Break Galaxies: Other Lensing Arcs around MS1512-cB58
We have obtained near-infrared spectra of two images of the galaxy at z=2.72 which is gravitationally lensed by the foreground cluster MS1512+36. The brighter arc, cB58, is an image of only the nucleus and the southern half of the background galaxy, while the fainter image, A2, encompasses the entire background galaxy. Thus the gravitational lensing provides spatial resolution on a smaller scale than is routinely available by other methods.
Our observations indicate no evidence for any systematic rotational velocity gradient across the face of this galaxy. The nucleus and outer regions of the galaxy do not differ in their gas reddening or excitation level, based on the identical Hα/5007 ratios. cB58 (which is more dominated by the nucleus) has relatively stronger continuum emission, perhaps because of a higher ratio of old to young stars, compared to the outer parts of the galaxy.
A second emission line source, denoted as K1, at a slightly lower redshift was serendipitously detected in the slit. It appears to be the gravitationally lensed image of another background galaxy in the same group as cB58
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