arXiv subjects

A. W. Blain

Publications and source records attributed to A. W. Blain.

At least 55 records · Page 3Linked to original sources

arXiv2012

A revised asteroid polarization-albedo relationship using WISE/NEOWISE data

We present a reanalysis of the relationship between asteroid albedo and polarization properties using the albedos derived from the Wide-field Infrared Survey Explorer. We find that the function that best describes this relation is a three-dimensional linear fit in the space of log(albedo)-log(polarization slope)-log(minimum polarization). When projected to two dimensions the parameters of the fit are consistent with those found in previous work. We also define p* as the quantity of maximal polarization variation when compared with albedo and present the best fitting albedo-p* relation. Some asteroid taxonomic types stand out in this three-dimensional space, notably the E, B, and M Tholen types, while others cluster in clumps coincident with the S- and C-complex bodies. We note that both low albedo and small (D<30 km) asteroids are under-represented in the polarimetric sample, and we encourage future polarimetric surveys to focus on these bodies.

astro-ph.EP↗

arXiv2011

A variable mid-infrared synchrotron break associated with the compact jet in GX 339-4

Many X-ray binaries remain undetected in the mid-infrared, a regime where emission from their compact jets is likely to dominate. Here, we report the detection of the black hole binary GX 339-4 with the Wide-field Infrared Survey Explorer (WISE) during a very bright, hard accretion state in 2010. Combined with a rich contemporaneous multiwavelength dataset, clear spectral curvature is found in the infrared, associated with the peak flux density expected from the compact jet. An optically-thin slope of ~-0.7 and a jet radiative power of >6x10^{35} erg/s (d/8 kpc)^2 are measured. A ~24 h WISE light curve shows dramatic variations in mid-infrared spectral slope on timescales at least as short as the satellite orbital period ~95 mins. There is also significant change during one pair of observations spaced by only 11 s. These variations imply that the spectral break associated with the transition from self-absorbed to optically-thin jet synchrotron radiation must be varying across the full wavelength range of ~3-22 microns that WISE is sensitive to, and more. Based on four-band simultaneous mid-infrared detections, the break lies at ~5x10^{13} Hz in at least two epochs of observation, consistent with a magnetic field B~1.5x10^4 G assuming a single-zone synchrotron emission region. The observed variability implies that either B, or the size of the acceleration zone above the jet base, are being modulated by factors of ~10 on relatively-short timescales.

astro-ph.HE↗

arXiv2011

Comparison of Millimeter-wave and X-Ray Emission in Seyfert Galaxies

We compare the emission at multiple wavelengths of an extended Seyfert galaxy sample, including both types of Seyfert nuclei. We use the Caltech Submillimeter Observatory to observe the CO J = 2-1 transition line in a sample of 45 Seyfert galaxies and detect 35 of them. The galaxies are selected by their joint soft X-ray (0.1-2.4 keV) and far-infrared (λ = 60-100 μm) emission from the ROSAT/IRAS sample. Since the CO line widths (W CO) reflect the orbital motion in the gravitational potential of the host galaxy, we study how the kinematics are affected by the central massive black hole (BH), using the X-ray luminosity. A significant correlation is found between the CO line width and hard (0.3-8 keV from Chandra and XMM-Newton) X-ray luminosity for both types of Seyfert nuclei. Assuming an Eddington accretion to estimate the BH mass (M BH) from the X-ray luminosity, the W CO-L X relation establishes a direct connection between the kinematics of the molecular gas of the host galaxy and the nuclear activity, and corroborates the previous studies that show that the CO is a good surrogate for the bulge mass. We also find a tight correlation between the (soft and hard) X-ray and the CO luminosities for both Seyfert types. These results indicate a direct relation between the molecular gas (i.e., star formation activity) of the host galaxy and the nuclear activity. To establish a clear causal connection between molecular gas and the fueling of nuclear activity, high-resolution maps (<100 pc) of the CO emission of our sample will be required and provided in a forthcoming Atacama Large Millimeter Array observation.

astro-ph.CO↗

arXiv2011

The redshift and nature of AzTEC/COSMOS 1: A starburst galaxy at z=4.6

Based on broad/narrow-band photometry and Keck DEIMOS spectroscopy we report a redshift of z=4.64-0.08+0.06 for AzTEC/COSMOS 1, the brightest sub-mm galaxy in the AzTEC/COSMOS field. In addition to the COSMOS-survey X-ray to radio data, we report observations of the source with Herschel/PACS (100, 160 micron), CSO/SHARC II (350 micron), CARMA and PdBI (3 mm). We do not detect CO(5-4) line emission in the covered redshift ranges, 4.56-4.76 (PdBI/CARMA) and 4.94-5.02 (CARMA). If the line is within this bandwidth, this sets 3sigma upper limits on the gas mass to <~8x10^9 M_Sol and <~5x10^10 M_Sol, respectively (assuming similar conditions as observed in z~2 SMGs). This could be explained by a low CO-excitation in the source. Our analysis of the UV-IR spectral energy distribution of AzTEC 1 shows that it is an extremely young (<~50 Myr), massive (M*~10^11 M_Sol), but compact (<~2 kpc) galaxy forming stars at a rate of ~1300 M_Sol/yr. Our results imply that AzTEC 1 is forming stars in a 'gravitationally bound' regime in which gravity prohibits the formation of a superwind, leading to matter accumulation within the galaxy and further generations of star formation.

astro-ph.CO↗

arXiv2011

Far infrared constraints on the contamination by dust obscured galaxies of high-z dropout searches

The spectral energy distributions (SED) of dusty galaxies at intermediate redshift may look similar to very high redshift galaxies in the optical/near infrared (NIR) domain. This can lead to the contamination of high redshift galaxy searches based on broad band optical/NIR photometry by lower redshift dusty galaxies as both kind of galaxies cannot be distinguished. The contamination rate could be as high as 50%. {This work shows how the far infrared (FIR) domain can help to recognize likely low-z interlopers in an optical/NIR search for high-z galaxies.} We analyse the FIR SEDs of two galaxies proposed as very high redshift ($z>7$) dropout candidates based on deep Hawk-I/VLT observations. The FIR SEDs are sampled with PACS/Herschel at 100 and 160\,$μ$m, with SPIRE/Herschel at 250, 350 and 500\,$μ$m and with LABOCA/APEX at 870\,$μ$m. We find that redshifts $>7$ would imply extreme FIR SEDs (with dust temperatures $>100$\,K and FIR luminosities $>10^{13}$\,$L_{\odot}$). At z$\sim$2, instead, the SEDs of both sources would be compatible with that of typical ULIRGs/SMGs. Considering all the data available for these sources from visible to FIR we re-estimate the redshifts and we find $z\sim$1.6--2.5. Due to the strong spectral breaks observed in these galaxies, standard templates from the literature fail to reproduce the visible-near IR part of the SEDs even when additional extinction is included. These sources resemble strongly dust obscured galaxies selected in Spitzer observations with extreme visible-to-FIR colors, and the galaxy GN10 at $z=4$. Galaxies with similar SEDs could contaminate other high redshift surveys.

astro-ph.CO↗

arXiv2011

The Stellar Mass Content of Submillimeter-Selected Galaxies

We present a new study of the stellar mass in a sample of ~ 70 submillimeter-selected galaxies (SMGs) with accurate spectroscopic redshifts. We fit combinations of stellar population synthesis models and power laws to the galaxies' observed-frame optical through mid-IR spectral energy distributions to separate stellar emission from non-stellar near-IR continuum. By separating the stellar emission from the non-stellar near-IR continuum, we find that ~ 50% of our sample have non-stellar continuum contributions of less than 10% in rest-frame H-band, but ~ 10% of our sample have non-stellar contributions greater than 50%. We find that the K-band luminosity of the non-stellar continuum emission is correlated with hard X-ray luminosity, indicating an AGN origin of the emission. Upon subtracting this AGN-contributed continuum component from all of the galaxies in our sample, we determine a lower median stellar mass for SMGs than previous studies, ~ 7 x 10^10 M_sun. We use constraints of the starburst time-scale from molecular gas studies to estimate the amount of fading our sample would undergo if they passively evolve after the starburst terminates. The results suggest that typical SMGs, while among the most massive galaxies at z ~ 2, are likely to produce descendants of similar mass and luminosity to L* galaxies in the local universe.

astro-ph.CO↗

arXiv2011

Luminous Starbursts in the Redshift Desert at z~1-2: Star Formation Rates, Masses & Evidence for Outflows

We present a spectroscopic catalogue of 40 luminous starburst galaxies at z=0.7--1.7 (median z=1.3). 19 of these are submillimetre galaxies (SMGs) and 21 are submillimetre-faint radio galaxies (SFRGs). This sample helps to fill in the redshift desert at z=1.2--1.7 in previous studies as well as probing a lower luminosity population of galaxies. Radio fluxes are used to determine star-formation rates for our sample which range from around 50 to 500 M$_\odot$ yr$^{-1}$ and are generally lower than those in z$\sim$2 SMGs. We identify nebular [OII] 3727 emission in the rest-UV spectra and use the linewidths to show that SMGs and SFRGs in our sample have larger linewidths and therefore dynamical masses than optically selected star-forming galaxies at similar redshifts. The linewidths are indistinguishable from those measured in the z$\sim$2 SMG populations suggesting little evolution in the dynamical masses of the galaxies between redshift 1--2. [NeV] and [NeIII] emission lines are identified in a subset of the spectra indicating the presence of an active galactic nucleus (AGN). In addition, a host of interstellar absorption lines corresponding to transitions of MgII and FeII ions are also detected. These features show up prominently in composite spectra and we use these composites to demonstrate that the absorption lines are present at an average blueshift of $-240\pm$50 kms$^{-1}$ relative to the systemic velocities of the galaxies derived from [OII]. This indicates the presence of large-scale outflowing interstellar gas in these systems (Abridged)

astro-ph.CO↗

arXiv2011

Molecular Gas in Submillimetre-Faint, Star-Forming Ultraluminous Galaxies at z>1

[abridged] We present interferometric CO observations of twelve z~2 submillimetre-faint, star-forming radio galaxies (SFRGs) which are thought to be ultraluminous infrared galaxies (ULIRGs) possibly dominated by warmer dust (T_dust ~> 40 K) than submillimetre galaxies (SMGs) of similar luminosities. Four other CO-observed SFRGs are included from the literature, and all observations are taken at the Plateau de Bure Interferometer (PdBI) in the compact configuration. Ten of the sixteen SFRGs observed in CO (63%) are detected at >4sigma with a mean inferred molecular gas mass of ~2*10^10 M_sun. SFRGs trend slightly above the local ULIRG L_FIR-L'_CO relation. Since SFRGs are about two times fainter in radio luminosity but exhibit similar CO luminosities to SMGs, this suggests SFRGs are slightly more efficient star formers than SMGs at the same redshifts. SFRGs also have a narrow mean CO line width, 320+-80km/s. SFRGs bridge the gap between properties of very luminous >5*10^12 L_sun SMGs and those of local ULIRGs and are consistent with intermediate stage major mergers. We suspect that more moderate-luminosity SMGs, not yet surveyed in CO, would show similar molecular gas properties to SFRGs. The AGN fraction of SFRGs is consistent with SMGs and is estimated to be 0.3+-0.1, suggesting that SFRGs are observed near the peak phase of star formation activity and not in a later, post-SMG enhanced AGN phase. This CO survey of SFRGs serves as a pilot project for the much more extensive survey of Herschel and SCUBA-2 selected sources which only partially overlap with SMGs. Better constraints on CO properties of a diverse high-z ULIRG population are needed from ALMA to determine the evolutionary origin of extreme starbursts, and what role ULIRGs serve in catalyzing the formation of massive stellar systems in the early Universe.

astro-ph.CO↗

arXiv2010

Improving the identification of high-z Herschel sources with position priors and optical/NIR and FIR/mm photometric redshifts

We present preliminary results about the detection of high redshift (U)LIRGs in the Bullet cluster field by the PACS and SPIRE instruments within the Herschel Lensing Survey (HLS) Program. We describe in detail a photometric procedure designed to recover robust fluxes and deblend faint Herschel sources near the confusion noise. The method is based on the use of the positions of Spitzer/MIPS 24 um sources as priors. Our catalogs are able to reliably (5 sigma) recover galaxies with fluxes above 6 and 10 mJy in the PACS 100 and 160 um channels, respectively, and 12 to 18 mJy in the SPIRE bands. We also obtain spectral energy distributions covering the optical through the far-infrared/millimeter spectral ranges of all the Herschel detected sources, and analyze them to obtain independent estimations of the photometric redshift based on either stellar population or dust emission models. We exemplify the potential of the combined use of Spitzer position priors plus independent optical and IR photometric redshifts to robustly assign optical/NIR counterparts to the sources detected by Herschel and other (sub-)mm instruments.

astro-ph.CO↗

arXiv2010

Deep Herschel view of obscured star formation in the Bullet cluster

We use deep, five band (100-500um) data from the Herschel Lensing Survey (HLS) to fully constrain the obscured star formation rate, SFR_FIR, of galaxies in the Bullet cluster (z=0.296), and a smaller background system (z=0.35) in the same field. Herschel detects 23 Bullet cluster members with a total SFR_FIR = 144 +/- 14 M_sun yr^-1. On average, the background system contains brighter far-infrared (FIR) galaxies, with ~50% higher SFR_FIR (21 galaxies; 207 +/- 9 M_sun yr^-1). SFRs extrapolated from 24um flux via recent templates (SFR_24) agree well with SFR_FIR for ~60% of the cluster galaxies. In the remaining ~40%, SFR_24 underestimates SFR_FIR due to a significant excess in observed S_100/S_24 (rest frame S_75/S_18) compared to templates of the same FIR luminosity.

astro-ph.CO↗

arXiv2010

First detection of the Sunyaev Zel'dovich effect increment at lambda < 650 um

The Sunyaev-Zel'dovich (SZ) effect is a spectral distortion of the cosmic microwave background as observed through the hot plasma in galaxy clusters. This distortion is a decrement in the CMB intensity for lambda > 1.3 mm, an increment at shorter wavelengths, and small again by lambda ~250 um. As part of the Herschel Lensing Survey (HLS) we have mapped 1E0657-56 (the Bullet cluster) with SPIRE with bands centered at 250, 350 and 500 um and have detected the SZ effect at the two longest wavelengths. The measured SZ effect increment central intensities are Delta I_{0} = 0.097 +- 0.019 MJy sr^{-1} at 350 um and Delta I_{0} = 0.268 +- 0.031 MJy sr^{-1} at 500 um, consistent with the SZ effect spectrum derived from previous measurements at 2 mm. No other diffuse emission is detected. The presence of the finite temperature SZ effect correction is preferred by the SPIRE data at a significance of 2.1 sigma, opening the possibility that the relativistic SZ effect correction can be constrained by SPIRE in a sample of clusters. The results presented here have important ramifications for both sub-mm measurements of galaxy clusters and blank field surveys with SPIRE.

astro-ph.CO↗

arXiv2010

The far-infrared/submillimeter properties of galaxies located behind the Bullet cluster

The Herschel Lensing Survey (HLS) takes advantage of gravitational lensing by massive galaxy clusters to sample a population of high-redshift galaxies which are too faint to be detected above the confusion limit of current far-infrared/submillimeter telescopes. Measurements from 100-500 micron bracket the peaks of the far-infrared spectral energy distributions of these galaxies, characterizing their infrared luminosities and star formation rates. We introduce initial results from our science demonstration phase observations, directed toward the Bullet cluster (1E0657-56). By combining our observations with LABOCA 870 micron and AzTEC 1.1 mm data we fully constrain the spectral energy distributions of 19 MIPS 24 micron selected galaxies which are located behind the cluster. We find that their colors are best fit using templates based on local galaxies with systematically lower infrared luminosities.This suggests that our sources are not like local ultra-luminous infrared galaxies in which vigorous star formation is contained in a compact highly dust-obscured region. Instead, they appear to be scaled up versions of lower luminosity local galaxies with star formation occurring on larger physical scales.

astro-ph.CO↗

arXiv2010

The Herschel Lensing Survey (HLS): overview

The Herschel Lensing Survey (HLS) will conduct deep PACS and SPIRE imaging of ~40 massive clusters of galaxies. The strong gravitational lensing power of these clusters will enable us to penetrate through the confusion noise, which sets the ultimate limit on our ability to probe the Universe with Herschel. Here, we present an overview of our survey and a summary of the major results from our Science Demonstration Phase (SDP) observations of the Bullet Cluster (z=0.297). The SDP data are rich, allowing us to study not only the background high-redshift galaxies (e.g., strongly lensed and distorted galaxies at z=2.8 and 3.2) but also the properties of cluster-member galaxies. Our preliminary analysis shows a great diversity of far-infrared/submillimeter spectral energy distributions (SEDs), indicating that we have much to learn with Herschel about the properties of galaxy SEDs. We have also detected the Sunyaev-Zel'dovich (SZ) effect increment with the SPIRE data. The success of this SDP program demonstrates the great potential of the Herschel Lensing Survey to produce exciting results in a variety of science areas.

astro-ph.CO↗

arXiv2010

The Herschel-ATLAS: Evolution of the 250um luminosity function out to z=0.5

We have determined the luminosity function of 250um-selected galaxies detected in the ~14 sq.deg science demonstration region of the Herschel-ATLAS project out to a redshift of z=0.5. Our findings very clearly show that the luminosity function evolves steadily out to this redshift. By selecting a sub-group of sources within a fixed luminosity interval where incompleteness effects are minimal, we have measured a smooth increase in the comoving 250um luminosity density out to z=0.2 where it is 3.6+1.4-0.9 times higher than the local value.

astro-ph.CO↗

arXiv2010

Herschel ATLAS: The cosmic star formation history of quasar host galaxies

We present a derivation of the star formation rate per comoving volume of quasar host galaxies, derived from stacking analyses of far-infrared to mm-wave photometry of quasars with redshifts 0 I_AB>-32. We use the science demonstration observations of the first ~16 deg^2 from the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) in which there are 240 quasars from the Sloan Digital Sky Survey (SDSS) and a further 171 from the 2dF-SDSS LRG and QSO (2SLAQ) survey. We supplement this data with a compilation of data from IRAS, ISO, Spitzer, SCUBA and MAMBO. H-ATLAS alone statistically detects the quasars in its survey area at >5sigma at 250, 350 and 500um. From the compilation as a whole we find striking evidence of downsizing in quasar host galaxy formation: low-luminosity quasars with absolute magnitudes in the range -22>I_AB>-24 have a comoving star formation rate (derived from 100um rest-frame luminosities) peaking between redshifts of 1 and 2, while high-luminosity quasars with I_AB<-26 have a maximum contribution to the star formation density at z~3. The volume-averaged star formation rate of -22>I_AB>-24 quasars evolves as (1+z)^{2.3 +/- 0.7} at z<2, but the evolution at higher luminosities is much faster reaching (1+z)^{10 +/- 1} at -26>I_AB>-28. We tentatively interpret this as a combination of a declining major merger rate with time and gas consumption reducing fuel for both black hole accretion and star formation.

astro-ph.CO↗

arXiv2010

Herschel and SCUBA-2 imaging and spectroscopy of a bright, lensed submillimetre galaxy at z = 2.3

We present a detailed analysis of the far-IR properties of the bright, lensed, z = 2.3, SMG, SMM J2135-0102, using new observations with Herschel, SCUBA-2 and the VLA. These data allow us to constrain the galaxy's SED and show that it has an intrinsic rest-frame 8-1000um luminosity, L(bol), of (2.3 +/- 0.2) x 10^12 L(sun) and a likely SFR of ~400 M(sun)/yr. The galaxy sits on the far-IR/radio correlation for far-IR-selected galaxies. At ~>70um, the SED can be described adequately by dust components with T(d) ~ 30 and 60K. Using SPIRE's Fourier Transform Spectrometer we report a detection of the [CII] 158um cooling line. If the [CII], CO and far-IR continuum arise in photo-dissociation regions, we derive a characteristic gas density, n ~ 10^3 cm^-3, and a far-UV radiation field, G_0, 10^3x stronger than the Milky Way. L([CII])/L(bol) is significantly higher than in local ULIRGs but similar to the values found in local star-forming galaxies and starburst nuclei. This is consistent with SMM J2135-0102 being powered by starburst clumps distributed across ~2 kpc, evidence that SMGs are not simply scaled-up ULIRGs. Our results show that SPIRE's FTS has the ability to measure the redshifts of distant, obscured galaxies via the blind detection of atomic cooling lines, but it will not be competitive with ground-based CO-line searches. It will, however, allow detailed study of the integrated properties of high-redshift galaxies, as well as the chemistry of their ISM, once more suitably bright candidates have been found.

astro-ph.CO↗

arXiv2010

Mid-infrared spectroscopy of candidate AGN-dominated submillimeter galaxies

Spitzer spectroscopy has revealed that ~80% of submm galaxies (SMGs) are starburst (SB) dominated in the mid-infrared. Here we focus on the remaining ~20% that show signs of harboring powerful active galactic nuclei (AGN). We have obtained Spitzer-IRS spectroscopy of a sample of eight SMGs which are candidates for harboring powerful AGN on the basis of IRAC color-selection (S8/S4.5>2; i.e. likely power-law mid-infrared SEDs). SMGs with an AGN dominating (>50%) their mid-infrared emission could represent `missing link' sources in an evolutionary sequence involving a major merger. First of all, we detect PAH features in all of the SMGs, indicating redshifts from 2.5-3.4, demonstrating the power of the mid-infrared to determine redshifts for these optically faint dusty galaxies. Secondly, we see signs of both star-formation (from the PAH features) and AGN activity (from continuum emission) in our sample: 62% of the sample are AGN-dominated in the mid-infrared with a median AGN content of 56%, compared with <30% on average for typical SMGs, revealing that our IRAC color selection has successfully singled out sources with proportionately more AGN emission than typical SB-dominated SMGs. However, we find that only about 10% of these AGN dominate the bolometric emission of the SMG when the results are extrapolated to longer infrared wavelengths, implying that AGN are not a significant power source to the SMG population overall, even when there is evidence in the mid-infrared for substantial AGN activity. When existing samples of mid-infrared AGN-dominated SMGs are considered, we find that S8/S4.5>1.65 works well at selecting mid-infrared energetically dominant AGN in SMGs, implying a duty cycle of ~15% if all SMGs go through a subsequent mid-infrared AGN-dominated phase in the proposed evolutionary sequence.

astro-ph.CO↗

arXiv2010

High-resolution CO and radio imaging of z~2 ULIRGs: extended CO structures, and implications for the universal star formation law

We present high spatial resolution (0.4", ~3.5 kpc) PdBI interferometric data on three ultra-luminous infrared galaxies (ULIRGs) at z~2: two submillimetre galaxies and one submillimetre faint star forming radio galaxy. The three galaxies have been ro- bustly detected in CO rotational transitions, either 12CO(J=4-3) or 12CO(J=3-2), allowing their sizes and gas masses to be accurately constrained. These are the highest spatial resolution observations observed to date (by a factor of ~2) for intermediate-excitation CO emission in z~2 ULIRGs. The galaxies appear extended over several resolution elements, having a mean radius of 3.7 kpc. High-resolution (0.3") combined MERLIN-VLA observations of their radio continua allow an analysis of the star formation behaviour of these galaxies, on comparable spatial scales to that of the CO observations. This 'matched beam' approach sheds light on the spatial distribution of both molecular gas and star formation, and we can therefore calculate accurate star formation rates and gas surface densities: this allows us to place the three systems in the context of a Kennicutt-Schmidt (KS)-style star formation law. We find a difference in size between the CO and radio emission regions, and as such we suggest that using the spatial extent of the CO emission region to estimate the surface density of star formation may lead to error. This size difference also causes the star formation efficiencies within systems to vary by up to a factor of 5. We also find, with our new accurate sizes, that SMGs lie significantly above the KS relation, indicating that stars are formed more efficiently in these extreme systems than in other high-z star forming galaxies.

astro-ph.CO↗