56 research outputs found
The Busy Man’s ArXiv
The presentation concerns arXiv.org, a repository of electronic preprints, including the need to filter the huge volume of discipline specific materials being added. Description of history of arXiv.org, submitting items, research disciplines included, usage statistics, download rates, and how to stay on top of publications in the field of interest. BMarXiv is suggested as a possible solution to the large volume of information
The Infrared Database of Extragalactic Observables from Spitzer I: the redshift catalog
This is the first of a series of papers on the Infrared Database of
Extragalactic Observables from Spitzer (IDEOS). In this work we describe the
identification of optical counterparts of the infrared sources detected in
Spitzer Infrared Spectrograph (IRS) observations, and the acquisition and
validation of redshifts. The IDEOS sample includes all the spectra from the
Cornell Atlas of Spitzer/IRS Sources (CASSIS) of galaxies beyond the Local
Group. Optical counterparts were identified from correlation of the extraction
coordinates with the NASA Extragalactic Database (NED). To confirm the optical
association and validate NED redshifts, we measure redshifts with unprecedented
accuracy on the IRS spectra ({\sigma}(dz/(1+z))=0.0011) by using an improved
version of the maximum combined pseudo-likelihood method (MCPL). We perform a
multi-stage verification of redshifts that considers alternate NED redshifts,
the MCPL redshift, and visual inspection of the IRS spectrum. The statistics is
as follows: the IDEOS sample contains 3361 galaxies at redshift 0<z<6.42 (mean:
0.48, median: 0.14). We confirm the default NED redshift for 2429 sources and
identify 124 with incorrect NED redshifts. We obtain IRS-based redshifts for
568 IDEOS sources without optical spectroscopic redshifts, including 228 with
no previous redshift measurements. We provide the entire IDEOS redshift catalog
in machine-readable formats. The catalog condenses our compilation and
verification effort, and includes our final evaluation on the most likely
redshift for each source, its origin, and reliability estimates.Comment: 11 pages, 6 figures, 1 table. Accepted for publication in MNRAS. Full
redshift table in machine-readable format available at
http://ideos.astro.cornell.edu/redshifts.htm
Strong C+ emission in galaxies at z~1-2: Evidence for cold flow accretion powered star formation in the early Universe
We have recently detected the [CII] 157.7 micron line in eight star forming
galaxies at redshifts 1 to 2 using the redshift(z) Early Universe Spectrometer
(ZEUS). Our sample targets star formation dominant sources detected in PAH
emission. This represents a significant addition to [CII] observations during
the epoch of peak star formation. We have augmented this survey with
observations of the [OI] 63 micron line and far infrared photometry from the
PACS and SPIRE Herschel instruments as well as Spitzer IRS spectra from the
literature showing PAH features. Our sources exhibit above average gas heating
efficiency, many with both [OI]/FIR and [CII]/FIR ~1% or more. The relatively
strong [CII] emission is consistent with our sources being dominated by star
formation powered PDRs, extending to kpc scales. We suggest that the star
formation mode in these systems follows a Schmidt-Kennicutt law similar to
local systems, but at a much higher rate due to molecular gas surface densities
10 to 100 times that of local star forming systems. The source of the high
molecular gas surface densities may be the infall of neutral gas from the
cosmic web. In addition to the high [CII]/FIR values, we also find high
[CII]/PAH ratios and, in at least one source, a cool dust temperature. This
source, SWIRE 4-5, bears a resemblance in these diagnostics to shocked regions
of Stephan's Quintet, suggesting that another mode of [CII] excitation in
addition to normal photoelectric heating may be contributing to the observed
[CII] line.Comment: Accepted for publication in Astrophysical Journal. To appear in
December 20, 2014, V797 - 2 issu
Spitzer Observations of Young Red Quasars
We present mid-infrared spectra and photometry of 13 redshift 0.4 < z < 1 dust reddened quasars obtained with Spitzer IRS and MIPS. We compare properties derived from their infrared spectral energy distributions (intrinsic active galactic nucleus (AGN) luminosity and far-infrared luminosity from star formation) to the host luminosities and morphologies from Hubble Space Telescope imaging, and black hole masses estimated from optical and/or near-infrared spectroscopy. Our results are broadly consistent with models in which most dust reddened quasars are an intermediate phase between a merger-driven starburst triggering a completely obscured AGN, and a normal, unreddened quasar. We find that many of our objects have high accretion rates, close to the Eddington limit. These objects tend to fall below the black hole mass-bulge luminosity relation as defined by local galaxies, whereas most of our low accretion rate objects are slightly above the local relation, as typical for normal quasars at these redshifts. Our observations are therefore most readily interpreted in a scenario in which galaxy stellar mass growth occurs first by about a factor of three in each merger/starburst event, followed sometime later by black hole growth by a similar amount. We do not, however, see any direct evidence for quasar feedback affecting star formation in our objects, for example, in the form of a relationship between accretion rate and star formation. Five of our objects, however, do show evidence for outflows in the [O III]5007 Ă… emission line profile, suggesting that the quasar activity is driving thermal winds in at least some members of our sample
Detections of Water Ice, Hydrocarbons, and 3.3 \u3cem\u3eÎĽ\u3c/em\u3em PAH in \u3cem\u3ez\u3c/em\u3e ~ 2 ULIRGs
We present the first detections of the 3 μm water ice and 3.4 μm amorphous hydrocarbon (HAC) absorption features in z ~ 2 ULIRGs. These are based on deep rest-frame 2-8 μm Spitzer Infrared Spectrograph spectra of 11 sources selected for their appreciable silicate absorption. The HAC-to-silicate ratio for our z ~ 2 sources is typically higher by a factor of 2-5 than that observed in the Milky Way. This HAC “excess” suggests compact nuclei with steep temperature gradients as opposed to predominantly host obscuration. Beside the above molecular absorption features, we detect the 3.3 μm polycyclic aromatic hydrocarbon (PAH) emission feature in one of our sources with three more individual spectra showing evidence for it. Stacking analysis suggests that water ice, hydrocarbons, and PAH are likely present in the bulk of this sample even when not individually detected. The most unexpected result of our study is the lack of clear detections of the 4.67 μm CO gas absorption feature. Only three of the sources show tentative signs of this feature at significantly lower levels than has been observed in local ULIRGs. Overall we find that the closest local analogs to our sources, in terms of 3-4 μm color, HAC-to-silicate and ice-to-silicate ratios, as well as low PAH equivalent widths, are sources dominated by deeply obscured nuclei. Such sources form only a small fraction of ULIRGs locally and are commonly believed to be dominated by buried active galactic nuclei (AGNs). Our sample suggests that, in an absolute number, such buried AGNs are at least an order of magnitude more common at z ~ 2 than today. The presence of PAH suggests that significant levels of star formation are present even if the obscured AGNs typically dominate the power budget
Spitzer Mid-Infrared Spectroscopy of Infrared Luminous Galaxies at z~2 II: Diagnostics
We present mid-IR spectral decomposition of a sample of 48 Spitzer-selected
ULIRGs spanning z~1-3 and likely L_IR~10^12-10^13Lsun. Our study aims at
quantifying the star-formation and AGN processes in these sources which recent
results suggest have evolved strongly between the observed epoch and today. To
do this, we study the mid-IR contribution of PAH emission, continuum, and
extinction. About 3/4 of our sample are continuum- (i.e. AGN) dominated
sources, but ~60% of these show PAH emission, suggesting the presence of
star-formation activity. These sources have redder mid-IR colors than typical
optically-selected quasars. About 25% of our sample have strong PAH emission,
but none are likely to be pure starbursts as reflected in their relatively high
5um hot dust continua. However, their steep 30um-to-14um slopes suggest that
star-formation might dominate the total infrared luminosity. Six of our z~2
sources have EW6.2>~0.3um and L_14um>~10^12Lsun (implying L_IR>~10^13Lsun). At
these luminosities, such high EW6.2 ULIRGs do not exist in the local Universe.
We find a median optical depth at 9.7um of =1.4. This is consistent
with local IRAS-selected ULIRGs, but differs from early results on
SCUBA-selected z~2 ULIRGs. Similar to local ULIRGs about 25% of our sample show
extreme obscuration (tau_9.7>~3) suggesting buried nuclei. In general, we find
that our sources are similar to local ULIRGs, but are an order of magnitude
more luminous. It is not clear whether our z~2 ULIRGs are simply scaled-up
versions of local ULIRGs, or subject to fundamentally different physical
processes.Comment: 60 pages, 15 figures, accepted for publication in Ap
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