Pasadena, CA, United States
Pasadena, CA, United States

Time filter

Source Type

Rodriguez-Gonzalvez C.,Us Planck Data Center | Chary R.R.,Us Planck Data Center | Muchovej S.,California Institute of Technology | Melin J.-B.,CEA Saclay Nuclear Research Center | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2017

We use a Bayesian software package to analyse CARMA-8 data towards 19 unconfirmed Planck Sunyaev-Zel'dovich-cluster candidates from Rodríguez-Gonzálvez et al. that are associated with significant overdensities in WISE. We use two cluster parameterizations, one based on a (fixed shape) generalized-NFW (gNFW) pressure profile and another on a β gas density profile (with varying shape parameters) to obtain parameter estimates from the CARMA-8 data for the nine CARMA-8-detected clusters. Results from the β model show that our cluster candidates exhibit a heterogeneous set of brightness-temperature profiles. Comparison of Planck and CARMA-8 measurements show good agreement in Y500 and an absence of obvious biases. Applying a Planck prior in Y500 to the CARMA-8 gNFW results reduces uncertainties in Y500 and Θ500 dramatically (by a factor > 4), relative to the independent Planck or CARMA-8 measurements. From this combined analysis, we find that our sample is comprised of massive (Y500 ranging from 3.3-0.2 +0.2 to 10-1.5 +1.1 ×10-4 arcmin2, sd=2.2×10-4), relatively compact (θ500 ranging from 2.1-0.3 +0.1 to 5.5+0.2 -0.8 arcmin, sd=1.0) systems. Spectroscopic Keck/MOSFIRE data confirmed a galaxy member of one of our cluster candidates at z = 0.565. At the preferred photometric redshift of 0.5, we estimate the cluster mass M500 ≈ 0.8 ± 0.2 × 1015M⊙. We here demonstrate a powerful technique to find massive clusters at intermediate (z ≳ 0.5) redshifts using a cross-correlation between Planck and WISE data, with high-resolution CARMA-8 follow-up. We also use the combined capabilities of Planck and CARMA-8 to obtain a dramatic reduction, by a factor of several, in parameter uncertainties. © 2016 The Authors.


Del Moro A.,Durham University | Alexander D.M.,Durham University | Mullaney J.R.,Durham University | Mullaney J.R.,University Paris Diderot | And 30 more authors.
Astronomy and Astrophysics | Year: 2012

Context. A tight correlation exists between far-infrared and radio emission for star-forming galaxies (SFGs), which seems to hold out to high redshifts (z≈2). Any excess of radio emission over that expected from star formation processes is most likely produced by an active galactic nucleus (AGN), often hidden by large amounts of dust and gas. Identifying these radio-excess sources will allow us to study a population of AGN unbiased by obscuration and thus find some of the most obscured, Compton-thick AGN, which are in large part unidentified even in the deepest X-ray and infrared (IR) surveys. Aims. We present here a new spectral energy distribution (SED) fitting approach that we adopt to select radio-excess sources amongst distant star-forming galaxies in the GOODS-Herschel (North) field and to reveal the presence of hidden, highly obscured AGN. Methods. Through extensive SED analysis of 458 galaxies with radio 1.4 GHz and mid-IR 24 μm detections using some of the deepest Chandra X-ray, Spitzer and Herschel infrared, and VLA radio data available to date, we have robustly identified a sample of 51 radio-excess AGN (∼1300 deg-2) out to redshift z≈3. These radio-excess AGN have a significantly lower far-IR/radio ratio (q<1.68, 3σ) than the typical relation observed for star-forming galaxies (q≈2.2). Results. We find that ≈45% of these radio-excess sources have a dominant AGN component in the mid-IR band, while for the remainders the excess radio emission is the only indicator of AGN activity. The presence of an AGN is also confirmed by the detection of a compact radio core in deep VLBI 1.4 GHz observations for eight of our radio-excess sources (≈16%; ≈66% of the VLBI detected sources in this field), with the excess radio flux measured from our SED analysis agreeing, to within a factor of two, with the radio core emission measured by VLBI. We find that the fraction of radio-excess AGN increases with X-ray luminosity reaching ∼60% at L X≈1044-1045 ergs-1, making these sources an important part of the total AGN population. However, almost half (24/51) of these radio-excess AGN are not detected in the deep Chandra X-ray data, suggesting that some of these sources might be heavily obscured. Amongst the radio-excess AGN we can distinguish three groups of objects: i) AGN clearly identified in infrared (and often in X-rays), a fraction of which are likely to be distant Compton-thick AGN; ii) moderate luminosity AGN (LX≲ 1043 ergs-1) hosted in strong star-forming galaxies; and iii) a small fraction of low accretion-rate AGN hosted in passive (i.e. weak or no star-forming) galaxies. We also find that the specific star formation rates (sSFRs) of the radio-excess AGN are on average lower that those observed for X-ray selected AGN hosts, indicating that our sources are forming stars more slowly than typical AGN hosts, and possibly their star formation is progressively quenching. © © ESO, 2012.


Weinzirl T.,University of Texas at Austin | Jogee S.,University of Texas at Austin | Conselice C.J.,University of Nottingham | Papovich C.,Texas A&M University | And 8 more authors.
Astrophysical Journal | Year: 2011

We present our results on the structure and activity of massive galaxies at z = 1-3 using one of the largest (166 with M* ⊙ ≥ 5 × 1010 M ⊙) and most diverse samples of massive galaxies derived from the GOODS-NICMOS survey: (1) Sérsic 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 ∼ 0. Approximately ∼40% of massive galaxies are ultracompact (r e ≤ 2kpc), compared to less than 1% at z ∼ 0. Furthermore, most (∼65%) systems at z = 2-3 have a low Sérsic index n ≤ 2, compared to 13% at z ∼ 0. We present evidence that the n ≤ 2 systems at z = 2-3 likely contain prominent disks, unlike most massive z ∼ 0 systems. (2) There is a correlation between structure and star formation rates (SFRs). The majority (85%) of non-active galactic nucleus (AGN) massive galaxies at z = 2-3, with SFR high enough to yield a 5σ (30 μJy) 24 μm Spitzer detection, have low n ≤ 2. Such n ≤ 2 systems host the highest SFR. (3) The frequency of AGNs is 40% at z = 2-3. Most (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, re ). Dry minor and major mergers may play an important role in this process. © 2011. The American Astronomical Society. All rights reserved.


Teplitz H.I.,Infrared Processing and Analysis Center | Chary R.,Us Planck Data Center | Elbaz D.,CEA Saclay Nuclear Research Center | Dickinson M.,National Optical Astronomy Observatory | And 12 more authors.
Astronomical Journal | Year: 2011

We present Spitzer 16μm imaging of the Great Observatories Origins Deep Survey (GOODS) fields. We survey 150 arcmin2 in each of the two GOODS fields (North and South), to an average 3σ depth of 40 and 65μJy, respectively. We detect ∼1300 sources in both fields combined. We validate the photometry using the 3-24μm spectral energy distribution of stars in the fields compared to Spitzer spectroscopic templates. Comparison with ISOCAM and AKARI observations in the same fields shows reasonable agreement, though the uncertainties are large. We provide a catalog of photometry, with sources cross-correlated with available Spitzer, Chandra, and Hubble Space Telescope data. Galaxy number counts show good agreement with previous results from ISOCAM and AKARI with improved uncertainties. We examine the 16-24μm flux ratio and find that for most sources it lies within the expected locus for starbursts and infrared luminous galaxies. A color cut of S16/S24 > 1.4 selects mostly sources which lie at 1.1 < z < 1.6, where the 24μm passband contains both the redshifted 9.7μm silicate absorption and the minimum between polycyclic aromatic hydrocarbon emission peaks.We measure the integrated galaxy light of 16μm sources and find a lower limit on the galaxy contribution to the extragalactic background light at this wavelength to be 2.2 ± 0.2 nWm-2 sr-1. © 2011 The American Astronomical Society. All rights reserved.


Perley D.A.,California Institute of Technology | Perley D.A.,Copenhagen University | Tanvir N.R.,University of Leicester | Hjorth J.,Copenhagen University | And 11 more authors.
Astrophysical Journal | Year: 2016

We present rest-frame near-IR (NIR) luminosities and stellar masses for a large and uniformly selected population of gamma-ray burst (GRB) host galaxies using deep Spitzer Space Telescope imaging of 119 targets from the Swift GRB Host Galaxy Legacy Survey spanning 0.03 < z < 6.3, and we determine the effects of galaxy evolution and chemical enrichment on the mass distribution of the GRB host population across cosmic history. We find a rapid increase in the characteristic NIR host luminosity between z ∼ 0.5 and z ∼ 1.5, but little variation between z ∼ 1.5 and z ∼ 5. 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 interstellar medium. Comparing our luminosity distributions with 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 small at z < 4. © 2016. The American Astronomical Society. All rights reserved..


Perley D.A.,California Institute of Technology | Perley D.A.,Copenhagen University | Kruhler T.,Copenhagen University | Kruhler T.,European Southern Observatory | And 24 more authors.
Astrophysical Journal | Year: 2016

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 (GRB) 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, multicolor optical/near-IR photometry, plus spectroscopy of events without preexisting 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 Using this sample, we estimate the redshift-dependent GRB rate density, showing it to peak at and fall by at least an order of magnitude toward low (z = 0) redshift, while declining more gradually toward high () 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. © 2016. The American Astronomical Society. All rights reserved..


Stroe A.,Leiden University | Shimwell T.,Leiden University | Rumsey C.,Astrophysics Group | Van Weeren R.,Harvard - Smithsonian Center for Astrophysics | And 8 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

Radio relics are patches of diffuse synchrotron radio emission that trace shock waves. Relics are thought to form when intracluster medium electrons are accelerated by cluster mergerinduced shock waves through the diffusive shock acceleration mechanism. In this paper, we present observations spanning 150 MHz to 30 GHz of the 'Sausage' and 'Toothbrush' relics from the Giant Metrewave and Westerbork telescopes, the Karl G. Jansky Very Large Array, the Effelsberg telescope, the Arcminute Microkelvin Imager and Combined Array for Research in Millimeter-wave Astronomy.We detect both relics at 30 GHz, where the previous highest frequency detection was at 16 GHz. The integrated radio spectra of both sources clearly steepen above 2 GHz, at the ≳6σ significance level, supporting the spectral steepening previously found in the 'Sausage' and the Abell 2256 relic. Our results challenge the widely adopted simple formation mechanism of radio relics and suggest more complicated models have to be developed that, for example, involve re-acceleration of aged seed electrons. © 2015 The Authors.


Rodriguez-Gonzalvez C.,Us Planck Data Center | Muchovej S.,California Institute of Technology | Chary R.R.,Us Planck Data Center
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present 1-2 arcmin spatial resolution Combined Array for Research in Millimetre-wave Astronomy (CARMA)-8 31 GHz observations towards 19 unconfirmed Planck cluster candidates, selected to have significant galaxy overdensities from the WISE early data release and thought to be at z ≳ 1 from the WISE colours of the putative brightest cluster galaxy. We find a Sunyaev-Zeldovich (SZ) detection in the CARMA-8 data towards nine candidate clusters, where one detection is considered tentative. For each cluster candidate we present CARMA-8 maps, a study of their radio-source environment and we assess the reliability of the SZ detection. The CARMA SZ detections appear to be SZ bright, with the mean, primary-beam-corrected peak flux density of the decrement being -2.9 mJy beam-1 with a standard deviation of 0.8, and are typically offset from the Planck position by ≈80 arcsec. Using archival imaging data in the vicinity of the CARMA SZ centroids, we present evidence that one cluster matches Abell 586 - a known z ≈ 0.2 cluster; four candidate clusters are likely to have 0.3 ≈ z ≈ 0.7; and, for the remaining four, the redshift information is inconclusive. We also argue that the sensitivity limits resulting from the cross-correlation between Planck and WISE makes it challenging to use our selection criterion to identify clusters at z > 1. © 2014 The Authors.


Chary R.,Us Planck Data Center | Petitjean P.,Institute Dastrophysique Of Paris | Robertson B.,University of California at Santa Cruz | Trenti M.,University of Melbourne | Vangioni E.,Institute Dastrophysique Of Paris
Space Science Reviews | Year: 2016

We review the uncertainties in high-z star-formation rate (SFR) measures and the constraints that one obtains from high-z gamma-ray burst (GRB) rates on them. We show that at the present time, the GRB rates per unit star-formation at (Formula presented.) are higher than at lower redshift. There could be a multitude of reasons for this: a stellar metallicity bias for GRB production, a top-heavy initial mass function (IMF) and/or missing a significant fraction of star-formation in field galaxy surveys due to incompleteness, surface brightness limitations and cosmic variance. We also compare metallicity predictions made using a hierarchical model of cosmic chemical evolution based on two recently proposed SFRs, one based on the observed galaxy luminosity function at high redshift and one based on the GRB rate and find that within the considerable scatter in metal abundance measures, they both are consistent with the data. Analyzing the ensemble of different measurements together, we conclude that despite metallicity biases, GRBs may be a less biased probe of star-formation at (Formula presented.) than at (Formula presented.). There is likely to be a common origin to the high GRB rate per unit star-formation and the high observed Lyman-continuum production rate in high redshift galaxies and that this may be due to a relative overabundance of stars with mass (Formula presented.) which are likely GRB progenitors. We also find that to reconcile these measurements with the Thomson scattering cross section of cosmic microwave background (CMB) photons measured by Planck, the escape fraction of Lyman-continuum photons from galaxies must be low, about ∼15 % or less and that the clumping factor of the IGM is likely to be small, ∼3. Finally, we demonstrate that GRBs are unique probes of metallicity evolution in low-mass galaxy samples and that GRB hosts likely lost a significant fraction of metals to the intergalactic medium (IGM) due to feedback processes such as stellar winds and supernovae. © 2016 Springer Science+Business Media Dordrecht


Kanekar N.,Tata Institute of Fundamental Research | Wagg J.,European Southern Observatory | Wagg J.,University of Cambridge | Chary R.R.,Us Planck Data Center | Carilli C.L.,U.S. National Radio Astronomy Observatory
Astrophysical Journal Letters | Year: 2013

We report a Plateau de Bure Interferometer search for C II 158 μm emission from HCM 6A, a lensed Lyα emitter (LAE) at z = 6.56. Our non-detections of C II 158 μm line emission and 1.2 mm radio continuum emission yield 3σ limits of LȮ for the C II 158 μm line luminosity and S 1.2 mm < 0.68 mJy for the 1.2 mm flux density. The local conversion factor between L C II and the star formation rate (SFR) yields an SFR < 4.7 MȮ yr-1, ≈2 times lower than that inferred from the ultraviolet (UV) continuum, suggesting that the local factor may not be applicable in high-z LAEs. The non-detection of 1.2 mm continuum emission yields a total SFR < 28 MȮ yr-1; any obscured star formation is thus within a factor of two of the visible star formation. Our best-fit model to the rest-frame UV/optical spectral energy distribution of HCM 6A yields a stellar mass of 1.3 × 109 MȮ and an SFR of ≈10 MȮ yr-1, with negligible dust obscuration. We fortuitously detect CO J = 3-2 emission from a z = 0.375 galaxy in the foreground cluster A370, and obtain a CO line luminosity of L′(CO) > (8.95 ± 0.79) × 108 K km s-1 pc2 and a molecular gas mass of M(H2) > (4.12 ± 0.36) × 109 MȮ, for a CO-to-H2 conversion factor of 4.6 MȮ (K km s-1 pc2)-1. © 2013. The American Astronomical Society. All rights reserved.

Loading Us Planck Data Center collaborators
Loading Us Planck Data Center collaborators