V. Desai

California Institute of Technology, Pasadena, California, United States

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Publications (103)328.9 Total impact

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    ABSTRACT: We present a detailed study of the colours in late-type galaxy discs for ten of the EDisCS galaxy clusters with 0.5 < z < 0.8. Our cluster sample contains 172 spiral galaxies, and our control sample is composed of 96 field disc galaxies. We deconvolve their ground-based V and I images obtained with FORS2 at the VLT with initial spatial resolutions between 0.4 and 0.8 arcsec to achieve a final resolution of 0.1 arcsec with 0.05 arcsec pixels, which is close to the resolution of the ACS at the HST. After removing the central region of each galaxy to avoid pollution by the bulges, we measured the V-I colours of the discs. We find that 50% of cluster spiral galaxies have disc V-I colours redder by more than 1 sigma of the mean colours of their field counterparts. This is well above the 16% expected for a normal distribution centred on the field disc properties. The prominence of galaxies with red discs depends neither on the mass of their parent cluster nor on the distance of the galaxies to the cluster cores. Passive spiral galaxies constitute 20% of our sample. These systems are not abnormally dusty. They are are made of old stars and are located on the cluster red sequences. Another 24% of our sample is composed of galaxies that are still active and star forming, but less so than galaxies with similar morphologies in the field. These galaxies are naturally located in the blue sequence of their parent cluster colour-magnitude diagrams. The reddest of the discs in clusters must have stopped forming stars more than ~5 Gyr ago. Some of them are found among infalling galaxies, suggesting preprocessing. Our results confirm that galaxies are able to continue forming stars for some significant period of time after being accreted into clusters, and suggest that star formation can decline on seemingly long (1 to 5 Gyr) timescales.
    No preview · Article · Jan 2016 · Astronomy and Astrophysics
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    ABSTRACT: We present results from a low-resolution spectroscopic survey for 21 galaxy clusters at 0.4<z<0.8 selected from the ESO Distant Cluster Survey (EDisCS). We measured spectra using the Low-Dispersion Prism (LDP) in IMACS on the Magellan Baade telescope and calculate redshifts with a precision of $\sigma_z=0.006$. We find 1,602 galaxies that are brighter than R=22.6 in the large-scale cluster environs. We identify the galaxies expected to be accreted by the clusters as they evolve to z=0 using spherical infall models, and find that ~30-70% of the z=0 cluster population lies outside the virial radius at z~0.6. For analogous clusters at z=0, we calculate that the ratio of galaxies that have fallen into the clusters since z~0.6 to that which were already in the core at that redshift is typically between ~0.3 and 1.5. This wide range of ratios is due to intrinsic scatter and is not a function of velocity dispersion, so a variety of infall histories is to be expected for clusters with current velocity dispersions of $300~<\sigma<~1200$ km/s. Within the infall regions of z~0.6 clusters, we find a larger red fraction of galaxies than in the field and greater clustering among red galaxies than blue. We interpret these findings as evidence of "preprocessing", where galaxies in denser local environments have their star formation rates affected prior to their aggregation into massive clusters, although the possibility of backsplash galaxies complicates the interpretation.
    Full-text · Article · Jun 2015
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    ABSTRACT: We present the Spitzer Archival Far-InfraRed Extragalactic Survey (SAFIRES). This program produces refined mosaics and source lists for all far-infrared extragalactic data taken during the more than six years of the cryogenic operation of the Spitzer Space Telescope. The SAFIRES products consist of far-infrared data in two wavelength bands (70 um and 160 um) across approximately 180 square degrees of sky, with source lists containing far-infrared fluxes for almost 40,000 extragalactic point sources. Thus, SAFIRES provides a large, robust archival far-infrared data set suitable for many scientific goals.
    Full-text · Article · Mar 2015 · The Astrophysical Journal Supplement Series
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    ABSTRACT: Ultra-faint star-forming galaxies produce a significant fraction of global star formation rate density at high redshifts. The magnification provided by strong gravitational lensing from massive clusters enables us to detect the faint background galaxies that are beyond our current detection limits. Using the massive lensing cluster Abell 1689 along with deep HST/WFC3 ultraviolet imaging (30 orbits in the F275W filter), we find that the UV luminosity function is steep down to very faint magnitudes (MUV = -13 AB mag) and shows no turnover. Our new HST program images Abell 1689 for 10 and 14 orbits in F225W and F336W bands, respectively. We again use the Lyman break technique to select star-forming galaxies as F225W and F336W “dropouts” at z=1.5 and z=2.7, respectively. Finally, we end up with a large sample of ultra-faint star-forming galaxies at the peak epoch of star formation, 1 < z < 3. We study the evolution of the faint-end slope of the UV luminosity function as well as a variety of properties of faint star-forming galaxies in this sample. We also measure the Lyman continuum escape fraction in these feeble sources, as they play an important role in making up the ionizing background radiation at both intermediate redshifts (1<z<3) and the epoch of reionization (z>6).
    No preview · Article · Jan 2014
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    ABSTRACT: We present a 48 orbit cycle-21 program to image three of the four Hubble Frontier Fields at near-ultraviolet wavelengths. Each lensing cluster will be observed for eight orbits in both the F275W and F336W filters. The primary science goals are to measure the luminosity functions of faint star-forming galaxies at 1.5<z<3, measure the Lyman continuum escape fractions, and study the sizes of star forming regions in galaxies at 1. Observations will likely begin in October. We will present the first images and compare to the existing optical Hubble images. In addition, we will show previous results from a deep near-UV imaging program in Abell 1689 as a demonstration of what can be done with these observations.
    No preview · Article · Jan 2014
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    ABSTRACT: We explore the relationship between gas, dust, and star formation in a sample of 12 ultraluminous 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 six 70 μm selected galaxies at z ~ 1 in order to quantify the properties of the molecular gas reservoir, the contribution of an active galactic nucleus (AGN) to the mid-IR luminosity, and the star formation efficiency (SFE = L IR/). 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 μm 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 L PAH, 6.2/L IR 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 L PAH, 6.2/L IR ratio at a given L IR 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 [C II] to molecular gas ratios in other studies suggests that PAH emission, like [C II], 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.
    Full-text · Article · Jun 2013 · The Astrophysical Journal
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    ABSTRACT: We use the Spitzer Space Telescope Enhanced Imaging Products (SEIP) and the Spitzer Archival Far-InfraRed Extragalactic Survey (SAFIRES) to study the spectral energy distributions of spectroscopically confirmed type 1 quasars selected from the Sloan Digital Sky Survey (SDSS). By combining the Spitzer and SDSS data with the 2-Micron All Sky Survey (2MASS) we are able to construct a statistically robust rest-frame 0.1-100 micron type 1 quasar template. We find the quasar population is well-described by a single power-law SED at wavelengths less than 20 microns, in good agreement with previous work. However, at longer wavelengths we find a significant excess in infrared luminosity above an extrapolated power-law, along with signifiant object-to-object dispersion in the SED. The mean excess reaches a maximum of 0.8 dex at rest-frame wavelengths near 100 microns.
    Full-text · Article · Mar 2013 · The Astrophysical Journal
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    ABSTRACT: We have obtained a deep (30-orbit) Hubble Space Telescope WFC3/UVIS F275W image of Abell 1689, a massive cluster at z=0.183, and one of the best studied HST targets for lensing surveys. We use the new UV data, in conjunction with existing high resolution optical and IR data to constrain the residual star-formation in the cluster early-type galaxy population, determine the ages of young stellar populations, providing insight into the buildup of the cluster red sequence.
    No preview · Article · Jan 2013
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    ABSTRACT: The NASA/IPAC Infrared Science Archive (IRSA) curates both data and analysis tools from NASA's infrared missions. As part of our primary goal, we provide long term access to mission-specific software from projects such as IRAS and Spitzer. We will review the efforts by IRSA (and within the greater IPAC before that) to keep the IRAS and Spitzer software tools current and available. Data analysis tools are a vital part of the Spitzer Heritage Archive. The IRAS tools HIRES and SCANPI have been in continual use since the 1980's. Scanpi offers a factor of 2 to 5 gain in sensitivity over the IRAS Point Source Catalog by performing 1D scan averaging of raw survey data at specified arbitrary position. In 2007 SCANPI was completely modernized, with major code revisions. HIRES returns IRAS survey images with higher resolution than the IRAS Sky Survey Atlas (ISSA). We are currently undertaking a modest revision to the tool to ensure continued reliability. In the next two years, the US Planck Data Center plans to adapt both tools for use with Planck data, and deliver them to IRSA for long term curation.
    No preview · Article · Sep 2012
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    ABSTRACT: 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_☉ <L_(IR)(8-1000 μm) 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.
    No preview · Article · May 2012
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    ABSTRACT: 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 (>1014M ☉) galaxy clusters. CO line emission is not detected in either DOG. We calculate 3σ upper limits to the CO J = 2-1 line luminosities, L'CO < 6.08 × 109 and <6.63 × 109 K km s–1 pc2. Assuming a CO-to-H2 conversion factor derived for ultraluminous infrared galaxies in the local universe, this translates to limits on the cold molecular gas mass of and . Both DOGs exhibit mid-infrared continuum emission that follows a power law, suggesting that an active galactic nucleus (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 < 7.4 × 1011L ☉, 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) × 1010 K km s–1 pc2, which leads to an estimated cold molecular gas mass . 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.
    Preview · Article · Apr 2012 · The Astrophysical Journal
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    ABSTRACT: Dust-obscured galaxies (DOGs) are a subset of high-redshift (z ≈ 2) optically-faint ultra-luminous infrared galaxies (ULIRGs, e.g., L IR > 1012L ☉). 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 1011.6L ☉ <L IR(8-1000 μm) < 1013.6L ☉. 90% of the Herschel-detected DOGs in this sample are ULIRGs and 30% have L IR > 1013L ☉. 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.
    Full-text · Article · Mar 2012 · The Astronomical Journal
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    ABSTRACT: The primary goal of the Local Cluster Survey is to measure the variations in the spatial extent of cold disk gas relative to the stellar disk for approximately 400 low-redshift group and cluster galaxies (z < 0.037) in order to quantify the relative importance of the physical mechanisms that cause galaxies to evolve from blue, actively star-forming galaxies to red, passive galaxies. The sample consists of 9 groups and clusters that span a range of X-ray luminosities, and all have optical photometry and spectroscopy from the SDSS, infrared 24-micron imaging from the Spitzer Space Telescope, and radio data from the ALFALFA survey. The wide areal coverage of these data allows us to track the evolution of disk gas from the dense cluster core to the surrounding field. Here we present a preliminary analysis of the stellar and gas radial profiles for the group and cluster galaxies. We compare with those of the surrounding field galaxies to look for signatures of environmentally-driven gas depletion.
    No preview · Article · Jan 2012
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    ABSTRACT: The Spitzer Science Center and NASA Infrared Science Archive (IRSA) will produce and release a set of Enhanced Imaging Products from the Spitzer Heritage Archive. We anticipate a preliminary release of a subset of the data in time for the January 2012 AAS. A release of the full set of products for the Spitzer cryogenic mission will fall in mid-to-late 2012. These products will include enhanced mosaics created using data from multiple programs where appropriate and a source list (SL) of photometry for compact sources. The primary requirement on the SL is very high reliability -- with areal coverage, completeness and limiting depth being secondary considerations. The enhanced imaging products will include data from the four channels of IRAC (3-8 microns) and the 24 micron channel of MIPS. The products will be generated for Spitzer observations of about 1500 square degrees and include around 30 million sources.
    No preview · Article · Jan 2012
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    ABSTRACT: The Spitzer Space Telescope has identified a population of ultraluminous infrared galaxies (ULIRGs) at z ~ 2 that may play an important role in the evolution of massive galaxies. We measure the stellar masses (M *) of two populations of Spitzer-selected ULIRGs that have extremely red R – [24] colors (dust-obscured galaxies, or DOGs) and compare our results with submillimeter-selected galaxies (SMGs). One set of 39 DOGs has a local maximum in their mid-infrared (mid-IR) spectral energy distribution (SED) at rest frame 1.6 μm associated with stellar emission ("bump DOGs"), while the other set of 51 DOGs have power-law mid-IR SEDs that are typical of obscured active galactic nuclei ("power-law DOGs"). We measure M * by applying Charlot & Bruzual stellar population synthesis models to broadband photometry in the rest-frame ultraviolet, optical, and near-infrared of each of these populations. Assuming a simple stellar population and a Chabrier initial mass function, we find that power-law DOGs and bump DOGs are on average a factor of 2 and 1.5 more massive than SMGs, respectively (median and inter-quartile M * values for SMGs, bump DOGs, and power-law DOGs are log(M */M ☉) = 10.42+0.42– 0.36, 10.62+0.36– 0.32, and 10.71+0.40– 0.34, respectively). More realistic star formation histories drawn from two competing theories for the nature of ULIRGs at z ~ 2 (major merger versus smooth accretion) can increase these mass estimates by up to 0.5 dex. A comparison of our stellar masses with the instantaneous star formation rate (SFR) in these z ~ 2 ULIRGs provides a preliminary indication supporting high SFRs for a given M *, a situation that arises more naturally in major mergers than in smooth accretion-powered systems.
    Full-text · Article · Dec 2011 · The Astrophysical Journal
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    ABSTRACT: The Spitzer Space Telescope has identified a population of ultra-luminous infrared galaxies (ULIRGs) at z ∼ 2 that may play an important role in the evolution of massive galaxies. We measure the stellar masses (M *) of two populations of Spitzer-selected ULIRGs that have extremely red R − [24] colors (dust-obscured galaxies, or DOGs) and compare our results with sub-millimeter selected galaxies (SMGs). One set of 39 DOGs have a local maximum in their mid-infrared (mid-IR) spectral energy distribution (SED) at rest-frame 1.6µm associated with stellar emission ("bump DOGs"), while the other set of 51 DOGs have power-law mid-IR SEDs that are typical of obscured AGN ("power-law DOGs"). We measure M * by applying Charlot & Bruzual stellar population synthesis models to broad-band photometry in the rest-frame ultra-violet, optical, and near-infrared of each of these populations. Assuming a simple stellar population and a Chabrier initial mass function (IMF), we find that power-law DOGs and bump DOGs are on average a factor of 2 and 1.5 larger than SMGs, respectively (median and inter-quartile M * values for SMGs, bump DOGs and power-law DOGs are log(M * /M ⊙) = 10.42 +0.42 −0.36 , 10.62 +0.36 −0.32 , and 10.71 +0.40 −0.34 , respectively). More realistic star-formation histories drawn from two competing theories for the nature of ULIRGs at z ∼ 2 (major merger vs. smooth accretion) can increase these mass estimates by up to 0.5 dex. A comparison of our stellar masses with the instantaneous star-formation rate (SFR) in these z ∼ 2 ULIRGs provides a preliminary indication supporting high SFRs for a given M * , a situation that arises more naturally in major mergers than in smooth accretion powered systems.
    Full-text · Article · Dec 2011
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    ABSTRACT: Exploiting the capabilities of four different surveys – the Padova–Millennium Galaxy and Group Catalogue (PM2GC), the WIde-field Nearby Galaxy-cluster Survey (WINGS), the IMACS (Inamori-Magellan Areal Camera and Spectrograph) Cluster Building Survey (ICBS) and the ESO (European Southern Observatory) Distant Cluster Survey (EDisCS) – we analyse the galaxy stellar mass distribution as a function of local density in mass-limited samples, in the field and in clusters from low () to high () redshift. We find that at all redshifts and in all environments, local density plays a role in shaping the mass distribution. In the field, it regulates the shape of the mass function at any mass above the mass limits. In clusters, it seems to be important only at low masses ( in WINGS and in EDisCS), otherwise it seems not to influence the mass distribution. Putting together our results with those of Calvi et al. and Vulcani et al. for the global environment, we argue that at least at local density is more important than global environment in determining the galaxy stellar mass distribution, suggesting that galaxy properties are not much dependent on halo mass, but do depend on local scale processes.
    Full-text · Article · Nov 2011 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: Detailed analysis of the substructure of Lya nebulae can put important constraints on the physical mechanisms at work and the properties of galaxies forming within them. Using high resolution HST imaging of a Lya nebula at z~2.656, we have taken a census of the compact galaxies in the vicinity, used optical/near-infrared colors to select system members, and put constraints on the morphology of the spatially-extended emission. The system is characterized by (a) a population of compact, low luminosity (~0.1 L*) sources --- 17 primarily young, small (Re~1-2 kpc), disky galaxies including an obscured AGN --- that are all substantially offset (>20 kpc) from the line-emitting nebula; (b) the lack of a central galaxy at or near the peak of the Lya emission; and (c) several nearly coincident, spatially extended emission components --- Lya, HeII, and UV continuum --- that are extremely smooth. These morphological findings are difficult to reconcile with theoretical models that invoke outflows, cold flows, or resonant scattering, suggesting that while all of these physical phenomena may be occurring, they are not sufficient to explain the powering and large extent of Lya nebulae. In addition, although the compact galaxies within the system are irrelevant as power sources, the region is significantly overdense relative to the field galaxy population (by at least a factor of 4). These observations provide the first estimate of the luminosity function of galaxies within an individual Lya nebula system, and suggest that large Lya nebulae may be the seeds of galaxy groups or low-mass clusters.
    Full-text · Article · Nov 2011 · The Astrophysical Journal

  • No preview · Article · Jul 2011
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    ABSTRACT: We present 3.6 and 4.5 μm Spitzer Infrared Array Camera (IRAC) imaging over 0.77 deg2 at the Virgo cluster core for the purpose of understanding the formation mechanisms of the low surface brightness intracluster light (ICL) features. Instrumental and astrophysical backgrounds that are hundreds of times higher than the signal were carefully characterized and removed. We examine ICL plumes as well as the outer halo of the giant elliptical M87. For two ICL plumes, we use optical colors to constrain their ages to be greater than 3 and 5 Gyr, respectively. Upper limits on the IRAC fluxes constrain the upper limits to the masses, and optical detections constrain the lower limits to the masses. In this first measurement of mass of ICL plumes we find masses in the range of 5.5 × 108 – 4.5 × 109 and 2.1 × 108-1.5 × 109M ☉ for the two plumes for which we have coverage. Given their expected short lifetimes, and a constant production rate for these types of streams, integrated over Virgo's lifetime, they can account for the total ICL content of the cluster, implying that we do not need to invoke ICL formation mechanisms other than gravitational mechanisms leading to bright plumes. We also examined the outer halo of the giant elliptical M87. The color profile from the inner to outer halo of M87 (160 kpc) is consistent with either a flat or optically blue gradient, where a blue gradient could be due to younger or lower metallicity stars at larger radii. The similarity of the age predicted by both the infrared and optical colors (> a few gigayears) indicates that the optical measurements are not strongly affected by dust extinction.
    Full-text · Article · Apr 2011 · The Astrophysical Journal

Publication Stats

2k Citations
328.90 Total Impact Points

Institutions

  • 1925-2015
    • California Institute of Technology
      • Spitzer Science Center
      Pasadena, California, United States
  • 2013
    • Paris Diderot University
      Lutetia Parisorum, Île-de-France, France
  • 2009
    • University of Kansas
      • Department of Physics and Astronomy
      Lawrence, Kansas, United States
    • University of Sussex
      • Astronomy Centre
      Brighton, England, United Kingdom
  • 2000-2009
    • University of Washington Seattle
      • Department of Astronomy
      Seattle, WA, United States
  • 2006
    • Cornell University
      • Department of Astronomy
      Ithaca, New York, United States
  • 2005
    • University of Crete
      • Department of Physics
      Retimo, Crete, Greece