Ranga-Ram Chary

California Institute of Technology, Pasadena, California, United States

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Publications (143)355.44 Total impact

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    ABSTRACT: The TMT Detailed Science Case describes the transformational science that the Thirty Meter Telescope will enable. Planned to begin science operations in 2024, TMT will open up opportunities for revolutionary discoveries in essentially every field of astronomy, astrophysics and cosmology, seeing much fainter objects much more clearly than existing telescopes. Per this capability, TMT's science agenda fills all of space and time, from nearby comets and asteroids, to exoplanets, to the most distant galaxies, and all the way back to the very first sources of light in the Universe. More than 150 astronomers from within the TMT partnership and beyond offered input in compiling the new 2015 Detailed Science Case. The contributing astronomers represent the entire TMT partnership, including the California Institute of Technology (Caltech), the Indian Institute of Astrophysics (IIA), the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC), the National Astronomical Observatory of Japan (NAOJ), the University of California, the Association of Canadian Universities for Research in Astronomy (ACURA) and US associate partner, the Association of Universities for Research in Astronomy (AURA).
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    ABSTRACT: We present rest-frame NIR luminosities and stellar masses for a large and uniformly-selected population of GRB host galaxies using deep Spitzer Space Telescope imaging of 117 targets from the Swift GRB Host Galaxy Legacy Survey spanning 0.03 < z < 6.3, and determine the effects of galaxy evolution and chemical enrichment on the mass distribution of the GRB host population across cosmic history. We find strong evolution in the host luminosity distribution between z~0.5 (median absolute NIR AB magnitude ~ -18.5, corresponding to M* ~ 3x10^8 M_sun and z~1.5), but negligible variation between z~1.5 and z~5 (median magnitude ~ -21.2, corresponding to M* ~ 5x10^9 M_sun). Dust-obscured GRBs dominate the massive host population but are only rarely seen associated with low-mass hosts, indicating that massive star-forming galaxies are universally and (to some extent) homogeneously dusty at high-redshift while low-mass star-forming galaxies retain little dust in their ISM. Comparing our luminosity distributions to field surveys and measurements of the high-z mass-metallicity relation, our results have good consistency with a model in which the GRB rate per unit star-formation is constant in galaxies with gas-phase metallicity below approximately the Solar value but heavily suppressed in more metal-rich environments. This model also naturally explains the previously-reported "excess" in the GRB rate beyond z>2; metals stifle GRB production in most galaxies at z<1.5 but have only minor impact at higher redshifts. The metallicity threshold we infer is much higher than predicted by single-star models and favors a binary progenitor. Our observations also constrain the fraction of cosmic star-formation in low-mass galaxies undetectable to Spitzer to be a small minority at most redshifts (~10% at z~2, ~25% at z~3, and ~50% at z=3.5-6.0).
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    ABSTRACT: We introduce the Swift Gamma-Ray Burst Host Galaxy Legacy Survey ("SHOALS"), a multi-observatory high-redshift galaxy survey targeting the largest unbiased sample of long-duration gamma-ray burst hosts yet assembled (119 in total). We describe the motivations of the survey and the development of our selection criteria, including an assessment of the impact of various observability metrics on the success rate of afterglow-based redshift measurement. We briefly outline our host-galaxy observational program, consisting of deep Spitzer/IRAC imaging of every field supplemented by similarly-deep, multi-color optical/NIR photometry, plus spectroscopy of events without pre-existing redshifts. Our optimized selection cuts combined with host-galaxy follow-up have so far enabled redshift measurements for 110 targets (92%) and placed upper limits on all but one of the remainder. About 20% of GRBs in the sample are heavily dust-obscured, and at most 2% originate from z>5.5. Using this sample we estimate the redshift-dependent GRB rate density, showing it to peak at z~2.5 and fall by about an order of magnitude towards low (z=0) redshift, while declining more gradually towards high (z~7) redshift. This behavior is consistent with a progenitor whose formation efficiency varies modestly over cosmic history. Our survey will permit the most detailed examination to date of the connection between the GRB host population and general star-forming galaxies, directly measure evolution in the host population over cosmic time and discern its causes, and provide new constraints on the fraction of cosmic star-formation occurring in undetectable galaxies at all redshifts.
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    ABSTRACT: Long-duration gamma-ray bursts act as beacons to the sites of star-formation in the distant universe. GRBs reveal galaxies too faint and star-forming regions too dusty to characterize in detail using any other method, and provide a powerful independent constraint on the evolution of the cosmic star-formation rate density at high-redshift. However, a full understanding of the GRB phenomenon and its relation to cosmic star-formation requires connecting the observations obtained from GRBs to the properties of the galaxies hosting them. The large majority of GRBs originate at moderate to high redshift (z>1) and Spitzer has proven crucial for understanding the host population, given its unique ability to observe the rest-frame NIR and its unrivaled sensitivity and efficiency. We propose to complete a comprehensive public legacy survey of the Swift GRB host population to build on our earlier successes and push beyond the statistical limits of previous, smaller efforts. Our survey will enable a diverse range of GRB and galaxy science including: (1) to quantitatively and robustly map the connection between GRBs and cosmic star-formation to constrain the GRB progenitor and calibrate GRB rate-based measurements of the high-z cosmic star-formation rate; (2) to constrain the luminosity function of star-forming galaxies at the faint end and at high redshift; (3) to understand how the ISM properties seen in absorption in high-redshift galaxies unveiled by GRBs - metallicity, dust column, dust properties - connect to global properties of the host galaxies such as mass and age. Building on a decade of experience at both observatories, our observations will create an enduring joint Swift-Spitzer legacy sample and provide the definitive resource with which to examine all aspects of the GRB/galaxy connection for years and possibly decades to come.
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    ABSTRACT: At which cosmic epoch did massive galaxy clusters assemble their baryons? How does star formation occur in the most massive, most rapidly collapsing dark-matter-dense environments in the early Universe? To answer these questions, we take the completely novel approach to select the most extreme z>~2 star-forming overdensities seen over the entire sky. This selection nicely complements the other existing selections for high redshift clusters (i.e., by stellar mass, or by total mass like Sunyaev-Zeldovish (SZ) or X-ray selection). We make use of the Planck all-sky submillimetre survey to systematically identify the rarest, most luminous high-redshift sub-mm sources on the sky, either strongly gravitationally lensed galaxies, or the joint FIR/sub-mm emission from multiple intense starbursts. We observed 228 Planck sources with Herschel/SPIRE and discovered that most of them are overdensities of red galaxies with extremely high star formation rates (typically 7.e3 Msun/yr for a structure). Only Spitzer data can allow a better understanding of these promising Planck+Herschel selected sources, as is shown on a first set of IRAC data on 40 targets in GO9: (i) the good angular resolution and sensitivity of IRAC allows a proper determination of the clustered nature of each Herschel/SPIRE source; (ii) IRAC photometry (often associated with J, K) allows a good estimate of the colors and approximate photometric redshift. Note spectroscopic redshifts are available for two cluster candidates, at z=1.7 and z=2.3, confirming their high redshift nature. The successful GO9 observation of 40 fields showed that about half to be >7sigma overdensities of red IRAC sources. These observations were targeting the whole range of Herschel overdensities and significances. We need to go deeper into the Spitzer sample and acquire complete coverage of the most extreme Herschel overdensities (54 new fields). Such a unique sample has legacy value, and this is the last opportunity prior to JWST, WFIRST and Euclid.
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    ABSTRACT: We report the detection of 6.2 μm polycyclic aromatic hydrocarbon (PAH) and rest-frame 4-7 μm continuum emission in the z = 4.055 submillimeter galaxy GN20, using the Infrared Spectrograph on board the Spitzer Space Telescope. This represents the first detection of PAH emission at z > 4. The strength of the PAH emission feature is consistent with a very high star formation rate of ~1600 M ☉ yr-1. We find that this intense starburst powers at least ~1/3 of the faint underlying 6 μm continuum emission, with an additional, significant (and perhaps dominant) contribution due to a power-law-like hot dust source, which we interpret to likely be a faint, dust-obscured active galactic nucleus (AGN). The inferred 6 μm AGN continuum luminosity is consistent with a sensitive upper limit on the hard X-ray emission as measured by the Chandra X-Ray Observatory if the previously undetected AGN is Compton-thick. This is in agreement with the finding at optical/infrared wavelengths that the galaxy and its nucleus are heavily dust-obscured. Despite the strong power-law component enhancing the mid-infrared continuum emission, the intense starburst associated with the photon-dominated regions that give rise to the PAH emission appears to dominate the total energy output in the infrared. GN20 is one of the most luminous starburst galaxies known at any redshift, embedded in a rich protocluster of star-forming galaxies. This investigation provides an improved understanding of the energy sources that power such exceptional systems, which represent the extreme end of massive galaxy formation at early cosmic times.
    The Astrophysical Journal 04/2014; 786(1). DOI:10.1088/0004-637X/786/1/31 · 6.28 Impact Factor
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    ABSTRACT: The first galaxies are the frontier of extragalactic astronomy. Hubble and Spitzer have measured the buildup of stellar mass and specific star formation rates from z ~ 8 to 4. Extending this to z > 9 with the handful of candidates discovered in the Hubble Ultra Deep Field has not been possible due to their faint observed fluxes (~10 nJy). We expect the upcoming Frontier Fields to deliver another ~35 - 120 candidates at z ~ 9 - 12. It is imperative that we learn more about their physical properties, but many will still be too faint for follow-up. Fortunately, CLASH, a shallower survey of gravitational lensing clusters, has yielded 4 much brighter z > 9 candidates, including the most distant: MACS0647-JD at z ~ 10.8 (observed 420 Myr after the Big Bang). Our primary target, lensed image MACS0647-JD2, is magnified by a factor of 7 to 170 nJy in the rest-frame UV. With an intrinsic (unlensed) flux of ~25 nJy, it is a near-analog of z > 9 candidates discovered in 'blank' (unlensed) Hubble deep fields. The existing Spitzer IRAC imaging (5 hours in each of ch1 3.6um and ch2 4.5um, PI Egami) yields no detection in ch1 but a possible (3-sigma) intriguing detection of a Balmer break / [OII] 3727A emission in ch2. Here we propose imaging 10 times deeper (50 hours in each band) to detect the object significantly in both channels and obtain the first constraints on the age, stellar mass, and rest-frame UV slope of a galaxy observed in the heart of the epoch of reionization. This imaging will also enable study of a large sample of ~30 lensed z ~ 6 - 8 candidates (far more than revealed by most other cluster lenses) with delensed intrinsic fluxes down to ~1 nJy. This study, now possible before JWST, will contribute to measurements of scatter about the 'main sequence of star formation,' constraining SFR duty cycles at these early times.
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    ABSTRACT: We report the detection of 6.2um polycyclic aromatic hydrocarbon (PAH) and rest-frame 4-7um continuum emission in the z=4.055 submillimeter galaxy GN20, using the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope. This represents the first detection of PAH emission at z>4. The strength of the PAH emission feature is consistent with a very high star formation rate of ~1800Msun/yr. We find that this intense starburst powers at least ~1/3 of the faint underlying 6um continuum emission, with an additional, significant (and perhaps dominant) contribution due to a power-law-like hot dust source, which we interpret to likely be a faint, dust-obscured active galactic nucleus (AGN). Despite the strong power-law component enhancing the mid-infrared continuum emission, the intense starburst associated with the photon-dominated regions that give rise to the PAH emission appears to dominate the total energy output in the infrared. By comparing the 6um AGN continuum luminosity to an upper limit on the hard X-ray emission as measured by the Chandra X-Ray Observatory, we also find evidence that the previously undetected AGN in this source is Compton-thick, consistent with the finding at optical/infrared wavelengths that the galaxy and its nucleus are heavily dust-obscured. GN20 is one of the most luminous starburst galaxies known at any redshift, embedded in a rich protocluster of star-forming galaxies. This investigation provides an improved understanding of the energy sources that power such exceptional systems, which represent the extreme end of massive galaxy formation at early cosmic times.
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    ABSTRACT: We explore the relationship between gas, dust and star formation in a sample of 12 ultra-luminous infrared galaxies (ULIRGs) at high redshift compared to a similar sample of local galaxies. We present new CO observations and/or Spitzer mid-IR spectroscopy for 6 70 micron selected galaxies at z~1 in order to quantify the properties of the molecular gas reservoir, the contribution of an active galactic nuclei (AGN) to the mid-IR luminosity and the star formation efficiency (SFE=LIR/L'CO). The mid-IR spectra show strong polycyclic aromatic hydrocarbon (PAH) emission and our spectral decomposition suggests that the AGN makes a minimal contribution (<25%) to the mid-IR luminosity. The 70 micron selected ULIRGs which we find to be spectroscopic close pairs, are observed to have high SFE, similar to local ULIRGs and high redshift submillimeter galaxies, consistent with enhanced IR luminosity due to an ongoing major merger. Combined with existing observations of local and high redshift ULIRGs, we further compare the PAH, IR and CO luminosities. We show that the ratio LPAH6.2/LIR decreases with increasing IR luminosity for both local and high redshift galaxies but the trend for high redshift galaxies is shifted to higher IR luminosities; the average LPAH6.2/LIR ratio at a given LIR is ~3 times higher at high redshift. When we normalize by the molecular gas, we find this trend to be uniform for galaxies at all redshifts and that the molecular gas is correlated with the PAH dust emission.The similar trends seen in the [CII] to molecular gas ratios in other studies suggests that PAH emission, like [CII], continues to be a good tracer of photodissociation regions even at high redshift. Together the CO, PAH and far-IR fine structure lines should be useful for constraining the interstellar medium conditions in high redshift galaxies.
    The Astrophysical Journal 06/2013; 772(2). DOI:10.1088/0004-637X/772/2/92 · 6.28 Impact Factor
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    ABSTRACT: Planck is the first FIR/sub-mm all sky survey with the sensitivity required to systematically identify the rarest, most luminous high-redshift sub-mm sources on the sky, either strongly gravitationally lensed galaxies, or the joint FIR/sub-mm emission from multiple intense starbursts as expected for the most massive, most rapidly collapsing dark-matter environments in the early Universe. We use a color selection to identify a population of 500 bright, high-fidelity Planck high-z candidates, 180 of which we are now following up with Herschel/SPIRE, including an extraordinary allocation of ``Must Do'' Director's Discretionary Time. All of our sources have typical SPIRE colors of high-z galaxies, and the redshifts of several have already been confirmed spectroscopically. We will use Spitzer/IRAC to identify and analyze the stellar counterparts of 35 of these sources, aided (but not replaced) by existing and scheduled ground-based optical/NIR photometry. This will allow us to measure photometric redshifts, stellar masses, star formation histories and stellar ages of these sources. We will search for candidate member galaxies of nascent galaxy clusters, and prepare detailed spectroscopic follow-up. At what cosmic epoch did massive galaxy clusters form most of their stars? Will we find that star formation is more or less vigorous in these galaxies compared to galaxies in the field? Is the upper end of the ``red sequence'' already in place? These are only some of the questions that IRAC will help us address.
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    ABSTRACT: Measurements of the stellar mass in galaxies to increasingly high redshifts provide us one of the most powerful ways of gauging early galaxy build-up. Combining ultra- deep IRAC imaging observations with deep WFC3/IR observations have allowed astronomers both to identify and estimate masses for sources out to redshifts as high as z~8. However, it has been difficult to extend such studies to even higher redshifts due to the incredible faintness and rarity of typical z~9-10 galaxies. One method for stepping beyond the normal S/N limitations is to take advantage of gravitational lensing by massive galaxy clusters to magnify faint z>8 sources, but to do so, we must know where the magnified sources lie. Fortunately, utilizing the huge investment of HST time in the 524-orbit CLASH program, we have been able to identify 100s of z~5-8 galaxies and even 4 extremely tantalizing z~9-11 galaxy candidates. To extend our measurement of galaxy masses to the earliest possible times, we require ultra-deep Spitzer observations on these candidates to accurately measure their rest-frame optical properties. While two of the z~9-11 candidates are the subject of deep IRAC observations as a result of an approved program, the other two will not be the subject of such observations. Given the considerable galaxy-to-galaxy variations in the mass-to-light ratio, ultra-deep Spitzer observations are needed for all four z~9-11 candidates to establish the typical properties of galaxies in this epoch. We propose to obtain such observations over the two z~9 candidates lacking such observations. Not only will our proposed observations substantially improve our ability to estimate the stellar mass density at z~9-11, but it will play a pivotal role in characterizing the stellar masses and other properties of 20-30 other gravitationally lensed z~4-8 galaxies behind these clusters.
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    ABSTRACT: This document summarizes the results of a community-based discussion of the potential science impact of the Mayall+BigBOSS highly multiplexed multi-object spectroscopic capability. The KPNO Mayall 4m telescope equipped with the DOE- and internationally-funded BigBOSS spectrograph offers one of the most cost-efficient ways of accomplishing many of the pressing scientific goals identified for this decade by the "New Worlds, New Horizons" report. The BigBOSS Key Project will place unprecedented constraints on cosmological parameters related to the expansion history of the universe. With the addition of an open (publicly funded) community access component, the scientific impact of BigBOSS can be extended to many important astrophysical questions related to the origin and evolution of galaxies, stars, and the IGM. Massive spectroscopy is the critical missing ingredient in numerous ongoing and planned ground- and space-based surveys, and BigBOSS is unique in its ability to provide this to the US community. BigBOSS data from community-led projects will play a vital role in the education and training of students and in maintaining US leadership in these fields of astrophysics. We urge the NSF-AST division to support community science with the BigBOSS multi-object spectrograph through the period of the BigBOSS survey in order to ensure public access to the extraordinary spectroscopic capability.
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    ABSTRACT: The host galaxies of long-duration GRBs are drawn from uniquely broad range of luminosities and redshifts. Thus they offer the possibility of studying the evolution of star-forming galaxies without the limitations of other luminosity-selected samples, which typically are increasingly biased towards the most massive systems at higher redshift. However, reaping the full benefits of this potential requires careful attention to the selection biases affecting host identification. To this end, we propose observations of a Legacy sample of 70 GRB host galaxies (an additional 70 have already been observed by Spitzer), in order to constrain the mass and luminosity function in GRB-selected galaxies at high redshift, including its dependence on redshift and on properties of the afterglow. Crucially, and unlike previous Spitzer surveys, this sample is carefully designed to be uniform and free of optical selection biases that have caused previous surveys to systematically under-represent the role of luminous, massive hosts. We also propose to extend to larger, more powerfully constraining samples the study of two science areas where Spitzer observations have recently shown spectacular success: the hosts of dust-obscured GRBs (which promise to further our understanding of the connection between GRBs and star-formation in the most luminous galaxies), and the evolution of the mass-metallicity relation at z>2 (for which GRB host observations provide particularly powerful constraints on high-z chemical evolution).
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    Hyunjin Shim, Ranga-Ram Chary
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    ABSTRACT: Strong Halpha Emitters (HAEs) dominate the z~4 Lyman-break galaxy population. We have identified local analogs of these HAEs using the Sloan Digital Sky Survey (SDSS). At z<0.4, only 0.04% of galaxies are classified as HAEs with Halpha equivalent widths (>500A) comparable to that of z~4 HAEs. Local HAEs have lower stellar mass and lower ultraviolet (UV) luminosity than z~4 HAEs, yet the Halpha-to-UV luminosity ratio as well as their specific star-formation rate is consistent with that of z~4 HAEs indicating that they are scaled down versions of high-z star-forming galaxies. Compared to the previously studied local analogs of z~2 Lyman break galaxies selected using rest-frame UV, local HAEs show similar UV luminosity surface density, weaker Dn(4000) breaks, lower metallicity and lower stellar mass. This supports the idea that local HAEs are less evolved galaxies than the traditional Lyman break analogs. We are not able to constrain if the star-formation history in local HAEs is powered by mergers or by cosmological cold flow accretion. However, in the stacked spectrum, local HAEs show a strong HeII4686 emission line suggesting a population of young (<10Myr), hot, massive stars similar to that seen in some Wolf-Rayet galaxies. Low [NII]/[OIII] line flux ratios imply that local HAEs are inconsistent with being systems that host bright AGN. Instead, it is highly likely that local HAEs are galaxies with an elevated ionization parameter, either due to a high electron density or large escape fraction of hydrogen ionizing photons as in the case for Wolf-Rayet galaxies.
    The Astrophysical Journal 05/2012; 765(1). DOI:10.1088/0004-637X/765/1/26 · 6.28 Impact Factor
  • SPIENewsroom 02/2012; DOI:10.1117/2.1201202.004144
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    ABSTRACT: While the most massive present-day galaxies are large systems dominated by spheroids of old stars that exhibit little on-going star formation, their progenitors at intermediate redshift are an area of active study. We investigate this issue using one of the largest, most diverse samples of massive galaxies at z=1-3 mapped by the GOODS-NICMOS survey. We find that massive (M*>5×1010 Msun) galaxies at z=2-3, when the Universe was 2-3 billion years old, are radically different in terms of rest-frame optical structure, star formation rate (SFR), and black hole activity. (1) As much as 40% of massive galaxies at z=2-3 have ultra-compact rest-frame optical sizes (half-light radius <2 kpc), while less than 1% of massive galaxies at z 0 are that small. On average, massive galaxies at z=2-3 are more compact by a factor of 3-4. Furthermore, unlike their local counterparts, a large population of massive galaxies at z=2-3 have shapes, structural properties (Sersic index n<2), and SFR activity that all favor the presence of a massive disky component over a spheroid. (2) Up to 40% of massive galaxies at z=2-3 host active black holes (AGN), which is at least an order of magnitude higher than at z 0. Furthermore, there is a fascinating correlation between structure, SFR, and AGN activity. Most disky structures have a significant (5σ) 24 μm Spitzer detection, and such disky systems host the highest SFR (53 to 1466 Msun yr-1). Most ( 65%) AGN hosts have disky morphologies. Ultra-compact galaxies appear quiescent in terms of AGN activity and SFR. (3) The question of how to transform the massive galaxies present 2-3 Gyr after the Big Bang into modern bulge-dominated E/S0s remains a challenge for the current paradigm of galaxy evolution. We discuss the role of major and minor mergers as well as gas accretion along cosmological filaments.
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    ABSTRACT: The Planck mission has the unique capability of finding systematically and on the whole sky the rarest, most luminous high redshift submm sources. These can be lensed objects or obscured star-forming proto-groups/clusters of galaxies containing many individual sources forming stars at very high rates. Our full sample of candidates contains about 1 source per 28 sq. deg., and already 3 candidates have been spectroscopically confirmed as interesting high-z sources: one is a potential proto-group at z2 (using Herschel/SPIRE/OT1 and CFHT, VLT/XSHOOTER and PDBI); and 2 others are z=3-5.2 strongly lensed galaxies in the H-ATLAS and around A773 in H LS. We were just granted (last week) Herschel OT2 SPIRE imaging time to target 70 Planck sources, as well as additional 21 sources with SCUBA2 to statistically study these extreme objects probing bright end of the high-z luminosity function. Are these sources mainly lensed galaxies or overdensities ? As part of a pilot study to prepare observations of the complete sample, we propose IRAC imaging (down to 1uJy and 1.8uJu 5sigma in channels 1 and 2) of the 20 most promising targets to constrain the photometric redshifts and to measure the stellar mass in galaxies associated with these structures. These sources have no obvious WISE counterparts. Spitzer/IRAC is the only instrument to image these obscured high-z structures efficiently at the necessary angular resolution and sensitivity. We believe that IRAC photometry is an essential component to understand the nature of these high-z structures to be observed by Herschel and SCUBA2 and is the first necessary step towards a further ambitious multi-wavelength follow-up program aiming at getting spectroscopic redshifts and full physical and dynamical diagnostics.
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    ABSTRACT: We present our results on the structure and activity of massive galaxies at z = 1-3 using one of the largest (166 with M-star >= 5 x 10(10) M-circle dot) and most diverse samples of massive galaxies derived from the GOODS-NICMOS survey: (1) Sersic fits to deep NIC3 F160W images indicate that the rest-frame optical structures of massive galaxies are very different at z = 2-3 compared to z similar to 0. Approximately 40% of massive galaxies are ultracompact (r(e) <= 2 kpc), compared to less than 1% at z similar to 0. Furthermore, most (similar to 65%) systems at z = 2-3 have a low Sersic index n <= 2, compared to similar to 13% at z similar to 0. We present evidence that the n <= 2 systems at z = 2-3 likely contain prominent disks, unlike most massive z similar to 0 systems. (2) There is a correlation between structure and star formation rates (SFRs). The majority (similar to 85%) of non-active galactic nucleus (AGN) massive galaxies at z = 2-3, with SFR high enough to yield a 5 sigma (30 mu Jy) 24 mu m Spitzer detection, have low n <= 2. Such n <= 2 systems host the highest SFR. (3) The frequency of AGNs is similar to 40% at z = 2-3. Most (similar to 65%) AGN hosts have disky (n <= 2) morphologies. Ultracompact galaxies appear quiescent in terms of both AGN activity and star formation. (4) Large stellar surface densities imply massive galaxies at z = 2-3 formed via rapid, highly dissipative events at z > 2. The large fraction of n <= 2 disky systems suggests cold mode accretion complements gas-rich major mergers at z > 2. In order for massive galaxies at z = 2-3 to evolve into present-day massive E/S0s, they need to significantly increase (n, r(e)). Dry minor and major mergers may play an important role in this process.
    The Astrophysical Journal 12/2011; 743(1). DOI:10.1088/0004-637X/743/1/87 · 6.28 Impact Factor
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    ABSTRACT: This paper describes the Hubble Space Telescope imaging data products and data reduction procedures for the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). This survey is designed to document the evolution of galaxies and black holes at z 1.5-8, and to study Type Ia supernovae at z > 1.5. Five premier multi-wavelength sky regions are selected, each with extensive multi-wavelength observations. The primary CANDELS data consist of imaging obtained in the Wide Field Camera 3 infrared channel (WFC3/IR) and the WFC3 ultraviolet/optical channel, along with the Advanced Camera for Surveys (ACS). The CANDELS/Deep survey covers ~125 arcmin2 within GOODS-N and GOODS-S, while the remainder consists of the CANDELS/Wide survey, achieving a total of ~800 arcmin2 across GOODS and three additional fields (Extended Groth Strip, COSMOS, and Ultra-Deep Survey). We summarize the observational aspects of the survey as motivated by the scientific goals and present a detailed description of the data reduction procedures and products from the survey. Our data reduction methods utilize the most up-to-date calibration files and image combination procedures. We have paid special attention to correcting a range of instrumental effects, including charge transfer efficiency degradation for ACS, removal of electronic bias-striping present in ACS data after Servicing Mission 4, and persistence effects and other artifacts in WFC3/IR. For each field, we release mosaics for individual epochs and eventual mosaics containing data from all epochs combined, to facilitate photometric variability studies and the deepest possible photometry. A more detailed overview of the science goals and observational design of the survey are presented in a companion paper.
    The Astrophysical Journal Supplement Series 12/2011; 197(2):36. DOI:10.1088/0067-0049/197/2/36 · 14.14 Impact Factor
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    ABSTRACT: A new set of color selection criteria (VJL) analogous with the BzK method is designed to select both star-forming galaxies (SFGs) and passively-evolving galaxies (PEGs) at 2.3<z<3.5 by using rest-frame UV--optical (V-J vs. J-L) colors. The criteria are thoroughly tested with theoretical stellar population synthesis models and real galaxies with spectroscopic redshifts to evaluate their efficiency and contamination. We apply the well-tested VJL criteria to the HST/WFC3 Early Release Science field and study the physical properties of selected galaxies. The redshift distribution of selected SFGs peaks at z~2.7, slightly lower than that of Lyman Break Galaxies at z~3. Comparing the observed mid-infrared fluxes of selected galaxies with the prediction of pure stellar emission, we find that our VJL method is effective at selecting massive dusty SFGs that are missed by the Lyman Break Technique. About half of the star formation in massive (M_{star}>10^{10}M_{Sun}) galaxies at 2.3<z<3.5 is contributed by dusty (extinction E(B-V)>0.4) SFGs, which however, only account for ~20% of the number density of massive SFGs. We also use the mid-infrared fluxes to clean our PEG sample, and find that galaxy size can be used as a secondary criterion to effectively eliminate the contamination of dusty SFGs. The redshift distribution of the cleaned PEG sample peaks at z~2.5. We find 6 PEG candidates at z>3 and discuss possible methods to distinguish them from dusty contamination. We conclude that at least part of our candidates are real PEGs at z~3, implying that this type of galaxies began to form their stars at z>5. We measure the integrated stellar mass density of PEGs at z~2.5 and set constraints on it at z>3. We find that the integrated stellar mass density grows by at least about factor of 10 in 1 Gyr at 3<z<5 and by another factor of 10 in next 3.5 Gyr (1<z<3).
    The Astrophysical Journal 10/2011; 749(2). DOI:10.1088/0004-637X/749/2/149 · 6.28 Impact Factor

Publication Stats

4k Citations
355.44 Total Impact Points

Institutions

  • 2005–2012
    • California Institute of Technology
      • Spitzer Science Center
      Pasadena, California, United States
    • University of Crete
      • Department of Physics
      Retimo, Crete, Greece
    • Observatoire de Paris
      Lutetia Parisorum, Île-de-France, France
  • 1996–2009
    • University of California, Los Angeles
      • • Department of Physics and Astronomy
      • • Division of Astronomy & Astrophysics
      Los Angeles, CA, United States
  • 2007
    • Princeton University
      • Department of Astrophysical Sciences
      Princeton, New Jersey, United States
    • National Optical Astronomy Observatory
      Tucson, Arizona, United States
  • 2004
    • Pennsylvania State University
      • Department of Astronomy and Astrophysics
      University Park, Maryland, United States
  • 2000–2001
    • University of California, Santa Cruz
      • Department of Astronomy and Astrophysics
      Santa Cruz, California, United States