arXiv subjects

R. -R. Chary

Publications and source records attributed to R. -R. Chary.

69 records · Page 4Linked to original sources

arXiv2011

GOODS-Herschel: an infrared main sequence for star-forming galaxies

We present the deepest far-IR observations obtained with Herschel and examine the 3-500um SEDs of galaxies at 0 3x10^10 Lsun kpc^-2) and a high specific SFR (i.e., SBs). The rest-frame, UV-2700A size of these distant SBs is typically half that of MS galaxies, supporting the correlation between star formation density and SB activity that is measured for the local sample. Locally, (U)LIRGs are systematically in the SB mode, whereas most distant (U)LIRGs form stars in the "normal" MS mode. This confusion between two modes of star formation is the cause of the so-called "mid-IR excess" population of galaxies found at z>1.5 by previous studies. MS galaxies have strong PAH emission line features, a broad far-IR bump resulting from a combination of dust temperatures (Tdust~15-50 K), and an effective Tdust~31 K, as derived from the peak wavelength of their IR SED. Galaxies in the SB regime instead exhibit weak PAH EW and a sharper far-IR bump with an effective Tdust~40 K. Finally, we present evidence that the mid-to-far IR emission of X-ray AGNs is predominantly produced by star formation and that candidate dusty AGNs with a power-law emission in the mid-IR systematically occur in compact, dusty SBs. After correcting for the effect of SBs on IR8, we identify new candidates for extremely obscured AGNs.

astro-ph.CO↗

arXiv2011

Planck Early Results. VII. The Early Release Compact Source Catalog

(Abridged) A brief description of the methodology of construction, contents and usage of the Planck Early Release Compact Source Catalogue (ERCSC), including the Early Cold Cores (ECC) and the Early Sunyaev-Zeldovich (ESZ) cluster catalogue is provided. The catalogue is based on data that consist of mapping the entire sky once and 60% of the sky a second time by Planck, thereby comprising the first high sensitivity radio/submillimetre observations of the entire sky. A Monte-Carlo algorithm based on the injection and extraction of artificial sources into the Planck maps was implemented to select reliable sources among all extracted candidates such that the cumulative reliability of the catalogue is >=90%. The 10sigma photometric flux density limit of the catalogue at |b|>30 deg is 0.49, 1.0, 0.67, 0.5, 0.33, 0.28, 0.25, 0.47 and 0.82 Jy at each of the nine frequencies between 30 and 857 GHz. Sources which are up to a factor of ~2 fainter than this limit, and which are present in "clean" regions of the Galaxy where the sky background due to emission from the interstellar medium is low, are included in the ERCSC if they meet the high reliability criterion. The Planck ERCSC sources have known associations to stars with dust shells, stellar cores, radio galaxies, blazars, infrared luminous galaxies and Galactic interstellar medium features. A significant fraction of unclassified sources are also present in the catalogs. In addition, two early release catalogs that contain 915 cold molecular cloud core candidates and 189 SZ cluster candidates that have been generated using multi-frequency algorithms are presented. The entire source list, with more than 15000 unique sources, is ripe for follow-up characterisation with Herschel, ATCA, VLA, SOFIA, ALMA and other ground-based observing facilities.

astro-ph.CO↗

arXiv2011

Planck Early Results VIII: The all-sky Early Sunyaev-Zeldovich cluster sample

We present the first all-sky sample of galaxy clusters detected blindly by the Planck satellite through the Sunyaev-Zeldovich (SZ) effect from its six highest frequencies. This early SZ (ESZ) sample is comprised of 189 candidates, which have a high signal-to-noise ratio ranging from 6 to 29. Its high reliability (purity above 95%) is further ensured by an extensive validation process based on Planck internal quality assessments and by external cross-identification and follow-up observations. Planck provides the first measured SZ signal for about 80% of the 169 previously-known ESZ clusters. Planck furthermore releases 30 new cluster candidates, amongst which 20 meet the ESZ signal-to-noise selection criterion. At the submission date, twelve of the 20 ESZ candidates were confirmed as new clusters, with eleven confirmed using XMM-Newton snapshot observations, most of them with disturbed morphologies and low luminosities. The ESZ clusters are mostly at moderate redshifts (86% with z below 0.3) and span more than a decade in mass, up to the rarest and most massive clusters with masses above 10^15 Msol.

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arXiv2011

Planck Early Results: The Planck mission

The European Space Agency's Planck satellite was launched on 14 May 2009, and has been surveying the sky stably and continuously since 13 August 2009. Its performance is well in line with expectations, and it will continue to gather scientific data until the end of its cryogenic lifetime. We give an overview of the history of Planck in its first year of operations, and describe some of the key performance aspects of the satellite. This paper is part of a package submitted in conjunction with Planck's Early Release Compact Source Catalogue, the first data product based on Planck to be released publicly. The package describes the scientific performance of the Planck payload, and presents results on a variety of astrophysical topics related to the sources included in the Catalogue, as well as selected topics on diffuse emission.

astro-ph.IM↗

arXiv2011

Planck Early Results: Statistical properties of extragalactic radio sources in the Planck Early Release Compact Source Catalogue

The data reported in Planck's Early Release Compact Source Catalogue (ERCSC) are exploited to measure the number counts (dN/dS) of extragalactic radio sources at 30, 44, 70, 100, 143 and 217 GHz. Due to the full-sky nature of the catalogue, this measurement extends to the rarest and brightest sources in the sky. At lower frequencies (30, 44, and 70 GHz) our counts are in very good agreement with estimates based on WMAP data, being somewhat deeper at 30 and 70 GHz, and somewhat shallower at 44 GHz. Planck's source counts at 143 and 217 GHz join smoothly with the fainter ones provided by the SPT and ACT surveys over small fractions of the sky. An analysis of source spectra, exploiting Planck's uniquely broad spectral coverage, finds clear evidence of a steepening of the mean spectral index above about 70 GHz. This implies that, at these frequencies, the contamination of the CMB power spectrum by radio sources below the detection limit is significantly lower than previously estimated.

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arXiv2011

An Accounting of the Dust-Obscured Star Formation and Accretion Histories Over the Last ~11~Billion Years

(Abridged) We report on an accounting of the star formation and accretion driven energetics of 24um detected sources in GOODS North. For sources having infrared (IR; 8-1000um) luminosities >3x10^12 L_sun when derived by fitting local SEDs to 24um photometry alone, we find these IR luminosity estimates to be a factor of ~4 times larger than those estimated when the SED fitting includes additional 16 and 70um data (and in some cases mid-infrared spectroscopy and 850um data). This discrepancy arises from the fact that high luminosity sources at z>>0 appear to have far- to mid-infrared ratios, as well as aromatic feature equivalent widths, typical of lower luminosity galaxies in the local Universe. Using our improved estimates for IR luminosity and AGN contributions, we investigate the evolution of the IR luminosity density versus redshift arising from star formation and AGN processes alone. We find that, within the uncertainties, the total star formation driven IR luminosity density is constant between 1.15 < z < 2.35, although our results suggest a slightly larger value at z>2. AGN appear to account for <18% of the total IR luminosity density integrated between 0< z < 2.35, contributing <25% at each epoch. LIRG appear to dominate the star formation rate (SFR) density along with normal star-forming galaxies (L_IR < 10^11 L_sun) between 0.6 < z < 1.15. Once beyond z >2, the contribution from ultraluminous infrared galaxies ULIRGs becomes comparable with that of LIRGs. Using our improved IR luminosity estimates, we find existing calibrations for UV extinction corrections based on measurements of the UV spectral slope typically overcorrect UV luminosities by a factor of ~2, on average, for our sample of 24um-selected sources; accordingly we have derived a new UV extinction correction more appropriate for our sample.

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arXiv2011

Planck Early Results: The Planck View of Nearby Galaxies

The all-sky coverage of the Planck Early Release Compact Source Catalogue (ERCSC) provides an unsurpassed survey of galaxies at submillimetre (submm) wavelengths, representing a major improvement in the numbers of galaxies detected, as well as the range of far-IR/submm wavelengths over which they have been observed. We here present the first results on the properties of nearby galaxies using these data. We match the ERCSC catalogue to IRAS-detected galaxies in the Imperial IRAS Faint Source Redshift Catalogue (IIFSCz), so that we can measure the spectral energy distributions (SEDs) of these objects from 60 to 850 microns. This produces a list of 1717 galaxies with reliable associations between Planck and IRAS, from which we select a subset of 468 for SED studies, namely those with strong detections in the three highest frequency Planck bands and no evidence of cirrus contamination. The SEDs are fitted using parametric dust models to determine the range of dust temperatures and emissivities. We find evidence for colder dust than has previously been found in external galaxies, with T<20K. Such cold temperatures are found using both the standard single temperature dust model with variable emissivity beta, or a two dust temperature model with beta fixed at 2. We also compare our results to studies of distant submm galaxies (SMGs) which have been claimed to contain cooler dust than their local counterparts. We find that including our sample of 468 galaxies significantly reduces the distinction between the two populations. Fits to SEDs of selected objects using more sophisticated templates derived from radiative transfer models confirm the presence of the colder dust found through parameteric fitting. We thus conclude that cold (T<20K) dust is a significant and largely unexplored component of many nearby galaxies.

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arXiv2011

Planck Early Results: The Galactic Cold Core Population revealed by the first all-sky survey

We present the statistical properties of the first version of the Cold Core Catalogue of Planck Objects (C3PO), in terms of their spatial distribution, temperature, distance, mass, and morphology. We also describe the statistics of the Early Cold Core Catalogue (ECC, delivered with the Early Release Compact Source Catalogue, ERCSC) that is the subset of the 915 most reliable detections of the complete catalogue. We have used the CoCoCoDeT algorithm to extract 10783 cold sources. Temperature and dust emission spectral index β values are derived using the fluxes in the IRAS 100 \mum band and the three highest frequency Planck bands. Temperature spans from 7K to 17K, and peaks around 13K. Data are not consistent with a constant value of β over the all temperature range. β ranges from 1.4 to 2.8 with a mean value around 2.1, and several possible scenarios are possible, including β(T) and the effect of multiple T components folded into the measurements. For one third of the objects the distances are obtained. Most of the detections are within 2 kpc in the Solar neighbourhood, but a few are at distances greater than 4 kpc. The cores are distributed from the deep Galactic plane, despite the confusion, to high latitudes (>30$^{\circle}$). The associated mass estimates range from 1 to $10^5$ solar masses. Using their physical properties these cold sources are shown to be cold clumps, defined as the intermediate cold sub-structures between clouds and cores. These cold clumps are not isolated but mostly organized in filaments associated with molecular clouds. The Cold Core Catalogue of Planck Objects (C3PO) is the first unbiased all-sky catalogue of cold objects. It gives an unprecedented statistical view to the properties of these potential pre-stellar clumps and offers a unique possibility for their classification in terms of their intrinsic properties and environment.

astro-ph.GA↗

arXiv2011

Planck early results: first assessment of the High Frequency Instrument in-flight performance

The Planck High Frequency Instrument (HFI) is designed to measure the temperature and polarization anisotropies of the Cosmic Microwave Background and galactic foregrounds in six wide bands centered at 100, 143, 217, 353, 545 and 857 GHz at an angular resolution of 10' (100 GHz), 7' (143 GHz), and 5' (217 GHz and higher). HFI has been operating flawlessly since launch on 14 May 2009. The bolometers cooled to 100 mK as planned. The settings of the readout electronics, such as the bolometer bias current, that optimize HFI's noise performance on orbit are nearly the same as the ones chosen during ground testing. Observations of Mars, Jupiter, and Saturn verified both the optical system and the time response of the detection chains. The optical beams are close to predictions from physical optics modeling. The time response of the detection chains is close to pre-launch measurements. The detectors suffer from an unexpected high flux of cosmic rays related to low solar activity. Due to the redundancy of Planck's observations strategy, the removal of a few percent of data contaminated by glitches does not affect significantly the sensitivity. The cosmic rays heat up significantly the bolometer plate and the modulation on periods of days to months of the heat load creates a common drift of all bolometer signals which do not affect the scientific capabilities. Only the high energy cosmic rays showers induce inhomogeneous heating which is a probable source of low frequency noise.

astro-ph.IM↗

arXiv2010

A mature cluster with X-ray emission at z=2.07

We report evidence of a fully established galaxy cluster at z=2.07, consisting of a ~20sigma overdensity of red, compact spheroidal galaxies spatially coinciding with extended X-ray emission detected with XMM-Newton. We use VLT VIMOS and FORS2 spectra and deep Subaru, VLT and Spitzer imaging to estimate the redshift of the structure from a prominent z=2.07 spectroscopic redshift spike of emission-line galaxies, concordant with the accurate 12-band photometric redshifts of the red galaxies. Using NICMOS and Keck AO observations, we find that the red galaxies have elliptical morphologies and compact cores. While they do not form a tight red sequence, their colours are consistent with that of a >1.3$~Gyr population observed at z~2.1. From an X-ray luminosity of .2*10^43 erg s^-1 and the stellar mass content of the red galaxy population, we estimate a halo mass of 5.3-8*10^13 Msun, comparable to the nearby Virgo cluster. These properties imply that this structure could be the most distant, mature cluster known to date and that X-ray luminous, elliptical-dominated clusters are already forming at substantially earlier epochs than previously known.

astro-ph.CO↗

arXiv2010

The Hubble Space Telescope GOODS NICMOS Survey: Overview and the Evolution of Massive Galaxies at 1.5 < z < 3

We present the details and early results from a deep near-infrared survey utilising the NICMOS instrument on the Hubble Space Telescope centred around massive M_* > 10^11 M_0 galaxies at 1.7 < z < 2.9 found within the Great Observatories Origins Deep Survey (GOODS) fields. The GOODS NICMOS Survey (GNS) was designed to obtain deep F160W (H-band) imaging of 80 of these massive galaxies, as well as other colour selected objects such as Lyman-break drop-outs, BzK objects, Distant Red Galaxies, EROs, Spitzer Selected EROs, BX/BM galaxies, as well as sub-mm galaxies. We present in this paper details of the observations, our sample selection, as well as a description of features of the massive galaxies found within our survey fields. This includes: photometric redshifts, rest-frame colours, and stellar masses. We furthermore provide an analysis of the selection methods for finding massive galaxies at high redshifts, including colour selection, and how galaxy populations selected through different methods overlap. We find that a single colour selection method cannot locate all of the massive galaxies, with no one method finding more than 70 percent. We however find that the combination of these colour methods finds nearly all the massive galaxies, as selected by photometric redshifts with the exception of apparently rare blue massive galaxies. By investigating the rest-frame (U-B) vs. M_B diagram for these galaxies we furthermore show that there exists a bimodality in colour-magnitude space at z < 2, driven by stellar mass, such that the most massive galaxies are systematically red up to z~2.5, while lower mass galaxies tend to be blue. We also discuss the number densities for galaxies with stellar masses M_* > 10^11 M_0, whereby we find an increase of a factor of eight between z = 3 and z = 1.5, demonstrating that this is an epoch when massive galaxies establish most of their mass.

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arXiv2010

Evolution of Dust Temperature of Galaxies through Cosmic Time as seen by Herschel

We study the dust properties of galaxies in the redshift range 0.1 0.5 with L_IR>5x10^{10} L_\odot, appears to be 2-5 K colder than that of AKARI-selected local galaxies with similar luminosities; and the dispersion in T_dust for high-z galaxies increases with L_IR due to the existence of cold galaxies that are not seen among local galaxies. We show that this large dispersion of the L_IR-T_dust relation can bridge the gap between local star-forming galaxies and high-z submillimeter galaxies (SMGs). We also find that three SMGs with very low T_dust (<20 K) covered in this study have close neighbouring sources with similar 24-\mum brightness, which could lead to an overestimation of FIR/(sub)millimeter fluxes of the SMGs.

astro-ph.CO↗

arXiv2010

Herschel unveils a puzzling uniformity of distant dusty galaxies

The Herschel Space Observatory enables us to accurately measure the bolometric output of starburst galaxies and active galactic nuclei (AGN) by directly sampling the peak of their far-infrared (IR) emission. Here we examine whether the spectral energy distribution (SED) and dust temperature of galaxies have strongly evolved since z~2.5. We use Herschel deep extragalactic surveys from 100 to 500um to compute total IR luminosities in galaxies down to the faintest levels, using PACS and SPIRE in the GOODS-North field (PEP and HerMES key programs). We show that measurements in the SPIRE bands can be used below the statistical confusion limit if information at higher spatial resolution is used to identify isolated galaxies whose flux is not boosted by bright neighbors. Below z~1.5, mid-IR extrapolations are correct for star-forming galaxies with a dispersion of only 40% (0.15dex), therefore similar to z~0 galaxies. This narrow distribution is puzzling when considering the range of physical processes that could have affected the SED of these galaxies. Extrapolations from only one of the 160um, 250um or 350um bands alone tend to overestimate the total IR luminosity. This may be explained by the lack of far-IR constraints around and above ~150um (rest-frame) on local templates. We also note that the dust temperature of luminous IR galaxies around z~1 is mildly colder by 10-15% than their local analogs and up to 20% for ULIRGs at z~1.6. Above z=1.5, distant galaxies are found to exhibit a substantially larger mid- over far-IR ratio, which could either result from stronger broad emission lines or warm dust continuum heated by a hidden AGN. Two thirds of the AGNs identified in the field with a measured redshift exhibit the same behavior as purely star-forming galaxies. Hence a large fraction of AGNs harbor star formation at very high SFR and in conditions similar to purely star-forming galaxies.

astro-ph.CO↗

arXiv2009

The Detection of Anomalous Dust Emission in the Nearby Galaxy NGC 6946

We report on the Ka-band (26-40 GHz) emission properties for 10 star-forming regions in the nearby galaxy NGC 6946. From a radio spectral decomposition, we find that the 33 GHz flux densities are typically dominated by thermal (free-free) radiation. However, we also detect excess Ka-band emission for an outer-disk star-forming region relative to what is expected given existing radio, submillimeter, and infrared data. Among the 10 targeted regions, measurable excess emission at 33 GHz is detected for half of them, but in only one region is the excess found to be statistically significant ($\approx7σ$). We interpret this as the first likely detection of so called `anomalous' dust emission outside of the Milky Way. We find that models explaining this feature as the result of dipole emission from rapidly rotating ultrasmall grains are able to reproduce the observations for reasonable interstellar medium conditions. While these results suggest that the use of Ka-band data as a measure of star formation activity in external galaxies may be complicated by the presence of anomalous dust, it is unclear how significant a factor this will be for globally integrated measurements as the excess emission accounts for $\la$10% of the total Ka-band flux density from all 10 regions.

astro-ph.CO↗

arXiv2009

Balancing the Energy Budget between Star-Formation and AGN in High Redshift Infrared Luminous Galaxies

(abridged) We present deep Spitzer mid-infrared spectroscopy, along with 16, 24, 70, and 850um photometry, for 22 galaxies located in GOODS-N. The sample spans a redshift range of 0.6 < z < 2.6, 24um flux densities between ~0.2-1.2 mJy, and consists of SMGs, AGN, and optically faint (z_AB > 25) sources. We find that IR luminosities derived by fitting local SEDs with 24um photometry alone are well matched to those when additional mid-infrared spectroscopic and longer wavelength photometric data is used for galaxies having z < 1.4 and 24um-derived IR luminosities typically > 3x10^12 L_sun. However, for galaxies in the redshift range between 1.4 < z < 2.6, typically having 24um-derived IR luminosities > 3x10^12 L_sun, IR luminosities are overestimated by an average factor of ~5 when SED fitting with 24um photometry alone. This result arises partly due to the fact that high redshift galaxies exhibit PAH EQWs that are large compared to local galaxies of similar luminosities. Using improved estimates for the IR luminosities of these sources, we investigate whether their IR emission is found to be in excess relative to that expected based on extinction corrected UV SFRs, possibly suggesting the presence of an obscured AGN. Through a spectral decomposition of IRS spectroscopic data, we are able to isolate the fraction of IR luminosity arising from an AGN as opposed to star formation activity. This fraction is only ~30% of the total IR luminosity among the entire sample, on average. Of the sources identified as having mid-infrared excesses, half are accounted for by using proper bolometric corrections while half show the presence of obscured AGN. We do not find evidence for evolution in the FIR-radio correlation over this redshift range, although the SMGs have IR/radio ratios which are, on average, ~3 times lower than the nominal value.

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