169 research outputs found
The Spectral Energy Distribution and Infrared Luminosities of z ≈ 2 Dust-obscured Galaxies from Herschel and Spitzer
Dust-obscured galaxies (DOGs) are a subset of high-redshift (z ≈ 2) optically-faint ultra-luminous infrared galaxies (ULIRGs, e.g., L_(IR) > 10^(12) L_☉). We present new far-infrared photometry, at 250, 350, and 500 μm (observed-frame), from the Herschel Space Telescope for a large sample of 113 DOGs with spectroscopically measured redshifts. Approximately 60% of the sample are detected in the far-IR. The Herschel photometry allows the first robust determinations of the total infrared luminosities of a large sample of DOGs, confirming their high IR luminosities, which range from 10^(11.6) L_☉ 10^(13) L_☉. The rest-frame near-IR (1-3 μm) spectral energy distributions (SEDs) of the Herschel-detected DOGs are predictors of their SEDs at longer wavelengths. DOGs with "power-law" SEDs in the rest-frame near-IR show observed-frame 250/24 μm flux density ratios similar to the QSO-like local ULIRG, Mrk 231. DOGs with a stellar "bump" in their rest-frame near-IR show observed-frame 250/24 μm flux density ratios similar to local star-bursting ULIRGs like NGC 6240. None show 250/24 μm flux density ratios similar to extreme local ULIRG, Arp 220; though three show 350/24 μm flux density ratios similar to Arp 220. For the Herschel-detected DOGs, accurate estimates (within ~25%) of total IR luminosity can be predicted from their rest-frame mid-IR data alone (e.g., from Spitzer observed-frame 24 μm luminosities). Herschel-detected DOGs tend to have a high ratio of infrared luminosity to rest-frame 8 μm luminosity (the IR8 = L_(IR)(8-1000 μm)/νL_ν(8 μm) parameter of Elbaz et al.). Instead of lying on the z = 1-2 "infrared main sequence" of star-forming galaxies (like typical LIRGs and ULIRGs at those epochs) the DOGs, especially large fractions of the bump sources, tend to lie in the starburst sequence. While, Herschel-detected DOGs are similar to scaled up versions of local ULIRGs in terms of 250/24 μm flux density ratio, and IR8, they tend to have cooler far-IR dust temperatures (20-40 K for DOGs versus 40-50 K for local ULIRGs) as measured by the rest-frame 80/115 μm flux density ratios (e.g., observed-frame 250/350 μm ratios at z = 2). DOGs that are not detected by Herschel appear to have lower observed-frame 250/24 μm ratios than the detected sample, either because of warmer dust temperatures, lower IR luminosities, or both
CO J=2-1 line emission in cluster galaxies at z~1: fueling star formation in dense environments
We present observations of CO J=2-1 line emission in infrared-luminous
cluster galaxies at z~1 using the IRAM Plateau de Bure Interferometer. Our two
primary targets are optically faint, dust-obscured galaxies (DOGs) found to lie
within 2 Mpc of the centers of two massive (>10^14 Msun) galaxy clusters. CO
line emission is not detected in either DOG. We calculate 3-sigma upper limits
to the CO J=2-1 line luminosities, L'_CO < 6.08x10^9 and < 6.63x10^9 K km/s
pc^2. Assuming a CO-to-H_2 conversion factor derived for ultraluminous infrared
galaxies in the local Universe, this translates to limits on the cold molecular
gas mass of M_H_2 < 4.86x10^9 Msun and M_H_2 < 5.30x10^9 Msun. Both DOGs
exhibit mid-infrared continuum emission that follows a power-law, suggesting
that an AGN contributes to the dust heating. As such, estimates of the star
formation efficiencies in these DOGs are uncertain. A third cluster member with
an infrared luminosity, L_IR < 7.4x10^11 Lsun, is serendipitously detected in
CO J=2-1 line emission in the field of one of the DOGs located roughly two
virial radii away from the cluster center. The optical spectrum of this object
suggests that it is likely an obscured AGN, and the measured CO line luminosity
is L'_CO = (1.94 +/- 0.35)x10^10 K km/s pc^2, which leads to an estimated cold
molecular gas mass M_H_2 = (1.55+/-0.28)x10^10 Msun. A significant reservoir of
molecular gas in a z~1 galaxy located away from the cluster center demonstrates
that the fuel can exist to drive an increase in star-formation and AGN activity
at the outskirts of high-redshift clusters.Comment: 22 pages, 4 figures; accepted for publication in Ap
Astro2020 APC white paper: Elevating the role of software as a product of the research enterprise
Software is a critical part of modern research, and yet there are insufficient mechanisms in the scholarly ecosystem to acknowledge, cite, and measure the impact of research software. The majority of academic fields rely on a one-dimensional credit model whereby academic articles (and their associated citations) are the dominant factor in the success of a researcher\u27s career. In the petabyte era of astronomical science, citing software and measuring its impact enables academia to retain and reward researchers that make significant software contributions. These highly skilled researchers must be retained to maximize the scientific return from petabyte-scale datasets. Evolving beyond the one-dimensional credit model requires overcoming several key challenges, including the current scholarly ecosystem and scientific culture issues. This white paper will present these challenges and suggest practical solutions for elevating the role of software as a product of the research enterprise
The Local Cluster Survey II: Disk-Dominated Cluster Galaxies with Suppressed Star Formation
We investigate the role of dense environments in suppressing star formation
by studying star-forming galaxies in
nine clusters from the Local Cluster Survey () and a large
comparison field sample drawn from the Sloan Digital Sky Survey. We compare the
star-formation rate (SFR) versus stellar mass relation as a function of
environment and morphology. After carefully controlling for mass, we find that
in all environments, the degree of SFR suppression increases with increasing
bulge-to-total (B/T) ratio. In addition, the SFRs of cluster and infall
galaxies at a fixed mass are more suppressed than their field counterparts at
all values of B/T. These results suggest a quenching mechanism that is linked
to bulge growth that operates in all environments and an additional mechanism
that further reduces the SFRs of galaxies in dense environments. We limit the
sample to galaxies to control for the trends with morphology and
find that the excess population of cluster galaxies with suppressed SFRs
persists. We model the timescale associated with the decline of SFRs in dense
environments and find that the observed SFRs of the cluster core galaxies are
consistent with a range of models including: a mechanism that acts slowly and
continuously over a long (2-5 Gyr) timescale, and a more rapid ( Gyr)
quenching event that occurs after a delay period of 1-6 Gyr. Quenching may
therefore start immediately after galaxies enter clusters.Comment: 17 pages, 12 figure
The Spitzer Source List
The Spitzer Science Center will produce a source list (SL) of photometry for a large subset of imaging data in the Spitzer Heritage Archive (SHA). The list will enable a large range of science projects. The primary requirement on the SL is very high reliability, with areal coverage, completeness and limiting depth being secondary considerations. The SHA at the NASA Infrared Science Archive (IRSA) will serve the SL as an enhanced data product. The SL will include data from the four channels of IRAC (3–8 microns) and the 24 micron channel of MIPS. The Source List will include image products (mosaics) and photometric data for Spitzer observations of about 1500 square degrees and include around 30 million sources. We describe the plans and timeline for development of the Spitzer Source List. We demonstrate the verification of the Source List pipeline using Spitzer Legacy catalogs at "truth tables". Finally, we discuss the range of use cases which will be supported
Clustering of Dust-Obscured Galaxies at z ~ 2
We present the angular autocorrelation function of 2603 dust-obscured
galaxies (DOGs) in the Bootes field of the NOAO Deep Wide-Field Survey. DOGs
are red, obscured galaxies, defined as having R-[24] \ge 14 (F_24/F_R \ga
1000). Spectroscopy indicates that they are located at 1.5 \la z \la 2.5. We
find strong clustering, with r_0 = 7.40^{+1.27}_{-0.84} Mpc/h for the full F_24
> 0.3 mJy sample. The clustering and space density of the DOGs are consistent
with those of submillimeter galaxies, suggestive of a connection between these
populations. We find evidence for luminosity-dependent clustering, with the
correlation length increasing to r_0 = 12.97^{+4.26}_{-2.64} Mpc/h for brighter
(F_24 > 0.6 mJy) DOGs. Bright DOGs also reside in richer environments than
fainter ones, suggesting these subsamples may not be drawn from the same parent
population. The clustering amplitudes imply average halo masses of log M =
12.2^{+0.3}_{-0.2} Msun for the full DOG sample, rising to log M =
13.0^{+0.4}_{-0.3} Msun for brighter DOGs. In a biased structure formation
scenario, the full DOG sample will, on average, evolve into ~ 3 L* present-day
galaxies, whereas the most luminous DOGs may evolve into brightest cluster
galaxies.Comment: ApJL in press; 4 pages, 3 figures, 1 tabl
Spitzer Mid-Infrared Spectroscopy of 70um-Selected Distant Luminous Infrared Galaxies
We present mid-infrared spectroscopy obtained with the Spitzer Space
Telescope of a sample of 11 optically faint, infrared luminous galaxies
selected from a Spitzer MIPS 70um imaging survey of the NDWFS Bootes field.
These are the first Spitzer IRS spectra presented of distant 70um-selected
sources. All the galaxies lie at redshifts 0.3<z<1.3 and have very large
infrared luminosities of L_IR~ 0.1-17 x 10^12 solar luminosities. Seven of the
galaxies exhibit strong emission features attributed to polycyclic aromatic
hydrocarbons (PAHs). The average IRS spectrum of these sources is
characteristic of classical starburst galaxies, but with much larger infrared
luminosities. The PAH luminosities of L(7.7) ~ 0.4 - 7 x 10^11 solar
luminosities imply star formation rates of ~ 40 - 720 solar masses per year.
Four of the galaxies show deep 9.7um silicate absorption features and no
significant PAH emission features (6.2um equivalent widths < 0.03um). The large
infrared luminosities and low f70/f24 flux density ratios suggests that these
sources have AGN as the dominant origin of their large mid-infrared
luminosities, although deeply embedded but luminous starbursts cannot be ruled
out. If the absorbed sources are AGN-dominated, a significant fraction of all
far-infrared bright, optically faint sources may be dominated by AGN.Comment: 8 Pages, ApJ accepte
Redshift Distribution of Extragalactic 24 micron Sources
We present the redshift distribution of a complete, unbiased sample of 24
micron sources down to fnu(24 micron) = 300 uJy (5-sigma). The sample consists
of 591 sources detected in the Bootes field of the NOAO Deep Wide-Field Survey.
We have obtained optical spectroscopic redshifts for 421 sources (71%). These
have a redshift distribution peaking at z~0.3, with a possible additional peak
at z~0.9, and objects detected out to z=4.5. The spectra of the remaining 170
(29%) exhibit no strong emission lines from which to determine a redshift. We
develop an algorithm to estimate the redshift distribution of these sources,
based on the assumption that they have emission lines but that these lines are
not observable due to the limited wavelength coverage of our spectroscopic
observations. The redshift distribution derived from all 591 sources exhibits
an additional peak of extremely luminous (L(8-1000 micron) > 3 x 10^{12} Lsun)
objects at z~2, consisting primarily of sources without observable emission
lines. We use optical line diagnostics and IRAC colors to estimate that 55% of
the sources within this peak are AGN-dominated. We compare our results to
published models of the evolution of infrared luminous galaxies. The models
which best reproduce our observations predict a large population of
star-formation dominated ULIRGs at z > 1.5 rather than the AGN-dominated
sources we observe.Comment: 21 pages, 11 figures; accepted for publication in Ap
The Environmental Dependence of the Evolving S0 Fraction
We reinvestigate the dramatic rise in the S0 fraction, f_S0, within clusters
since z ~ 0.5. In particular, we focus on the role of the global galaxy
environment on f_S0 by compiling, either from our own observations or the
literature, robust line-of-sight velocity dispersions, sigma's, for a sample of
galaxy groups and clusters at 0.1 < z < 0.8 that have uniformly determined,
published morphological fractions. We find that the trend of f_S0 with redshift
is twice as strong for sigma < 750 km/s groups/poor clusters than for
higher-sigma, rich clusters. From this result, we infer that over this redshift
range galaxy-galaxy interactions, which are more effective in lower-sigma
environments, are more responsible for transforming spiral galaxies into S0's
than galaxy-environment processes, which are more effective in higher-sigma
environments. The rapid, recent growth of the S0 population in groups and poor
clusters implies that large numbers of progenitors exist in low-sigma systems
at modest redshifts (~ 0.5), where morphologies and internal kinematics are
within the measurement range of current technology.Comment: Accepted for publication in The Astrophysical Journal. 13 pages, 6
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