Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe multiplicity of 250-$mu$m Herschel sources in the COSMOS field
71
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We investigate the multiplicity of extragalactic sources detected by the Herschel Space Observatory in the COSMOS field. Using 3.6- and 24-$mu$m catalogues, in conjunction with 250-$mu$m data from Herschel, we seek to determine if a significant fraction of Herschel sources are composed of multiple components emitting at 250 $mu$m. We use the XID+ code, using Bayesian inference methods to produce probability distributions of the possible contributions to the observed 250-$mu$m flux for each potential component. The fraction of Herschel flux assigned to the brightest component is highest for sources with total 250-$mu$m fluxes < 45 mJy; however, the flux in the brightest component is still highest in the brightest Herschel sources. The faintest 250-$mu$m sources (30-45 mJy) have the majority of their flux assigned to a single bright component; the second brightest component is typically significantly weaker, and contains the remainder of the 250-$mu$m source flux. At the highest 250-$mu$m fluxes (45-110 mJy), the brightest and second brightest components are assigned roughly equal fluxes, and together are insufficient to reach 100 per cent of the 250-$mu$m source flux. This indicates that additional components are required, beyond the brightest two components, to reproduce the observed flux. 95 per cent of the sources in our sample have a second component that contains more than 10 per cent of the total source flux. Particularly for the brightest Herschel sources, assigning the total flux to a single source may overestimate the flux contributed by around 150 per cent.
rate research
Read More
The cosmic infrared background (CIB) provides a fundamental observational constraint on the star-formation history of galaxies over cosmic history. We estimate the contribution to the CIB from catalogued galaxies in the COSMOS field by using a novel map fitting technique on the textit{Herschel} SPIRE maps. Prior galaxy positions are obtained using detections over a large range in wavelengths in the $K_{rm s}$--3,GHz range. Our method simultaneously fits the galaxies, the system foreground, and the leakage of flux from galaxies located in masked areas and corrects for an over-fitting effect not previously accounted for in stacking methods. We explore the contribution to the CIB as a function of galaxy survey wavelength and depth. We find high contributions to the CIB with the deep $r$ ($m_{rm AB} le 26.5$), $K_{rm s}$ ($m_{rm AB} le 24.0$) and 3.6,$mu$m ($m_{rm AB} le 25.5$) catalogues. We combine these three deep catalogues and find a total CIB contributions of 10.5 $pm$ 1.6, 6.7 $pm$ 1.5 and 3.1 $pm$ 0.7,nWm$^{-2}$sr$^{-1}$ at 250, 350 and 500,$mu$m, respectively. Our CIB estimates are consistent with recent phenomenological models, prior based SPIRE number counts and with (though more precise than) the diffuse total measured by FIRAS. Our results raise the interesting prospect that the CIB contribution at $lambda le 500,mu$m from known galaxies has converged. Future large-area surveys like those with the Large Synoptic Survey Telescope are therefore likely to resolve a substantial fraction of the population responsible for the CIB at 250,$mu$m $leq lambda leq$ 500,$mu$m.
In this paper, we investigate the physical associations between blended far-infrared (FIR)-emitting galaxies, in order to identify the level of line-of-sight projection contamination in the single-dish Herschel data. Building on previous work, and as part of the Herschel Extragalactic Legacy Project (HELP), we identify a sample of galaxies in the COSMOS field which are found to be both FIR-bright (typically $sim 15$ mJy) and blended within the Herschel 250 $mu$m beam. We identify a spectroscopic or photometric redshift for each FIR-bright source. We conduct a joint probability distribution analysis on the redshift probability density functions to determine the fraction of the FIR sources with multiple FIR-bright counterparts which are likely to be found at consistent ($Delta z$ $< 0.01$) redshifts. We find that only 3 (0.4 per cent) of the pair permutations between counterparts are $>50$ per cent likely to be at consistent redshifts. A majority of counterparts (72 per cent) have no overlap in their redshift probability distributions whatsoever. This is in good agreement with the results of recent simulations, which indicate that single-dish observations of the FIR sky should be strongly contaminated by line of sight projection effects. We conclude that for our sample of 3.6- and 24-$mu$m selected, FIR-bright objects in the COSMOS field, the overwhelming majority of multi-component FIR systems are line of sight projections within the 18.1 arcsec Herschel beam, rather than physical associations.
Evolutionary properties of infrared (IR) luminous galaxies are important keys to understand dust-obscured star formation history and galaxy evolution. Based on the near- to mid-IR imaging with 9 continuous filters of AKARI space telescope, we present the characteristics of dusty star-forming (SF) galalxies showing polycyclic aromatic hydrocarbon (PAH) features observed by the North Ecliptic Pole (NEP) wide field survey of AKARI and Herschel. All the sample galaxies from the AKARI/NEP-Wide data are selected based both on the Herschel/SPIRE 250 {mu}m detection and optical spectroscopic redshift data. The physical modelling of spectral energy distribution (SED) using all available data points from u to sub-mm 500 {mu}m band, including WISE and PACS data where available, takes unique advantages of the continuous near to mid-IR coverage, reliable constraint on far-IR peak, spectroscopically determined accurate redshifts, as well as energy balance principle by MAGPHYS. This enables us to derive physically meaningful and accurate total infrared luminosity and 8 {mu}m (or PAH) luminosity consistently. Our sample galaxies are in the redshift range z <1, and majority of them appear to be normal SF/spiral populations showing PAH features near the 8 {mu}m. These SF galaxies showing PAHs in the mid-IR include various types from quiescent to starbursts. Some of our sample show shortage of 8 {mu}m luminosity compared to the total IR luminosity and this PAH deficit gets severe in more luminous IR galaxies, suggesting PAH molecules in these galaxies destroyed by strong radiation field from SF region or a large amount of cold dust in ISM. The specific SFR of our sample shows mass dependent time evolution which is consistent with downsizing evolutionary pattern.
We present an ALMA study of the ~180 brightest sources in the SCUBA-2 map of the COSMOS field from the S2COSMOS survey, as a pilot study for AS2COSMOS - a full survey of the ~1,000 sources in this field. In this pilot we have obtained 870-um continuum maps of an essentially complete sample of the brightest 182 sub-millimetre sources (S_850um=6.2mJy) in COSMOS. Our ALMA maps detect 260 sub-millimetre galaxies (SMGs) spanning a range in flux density of S_870um=0.7-19.2mJy. We detect more than one SMG counterpart in 34+/-2 per cent of sub-millimetre sources, increasing to 53+/-8 per cent for SCUBA-2 sources brighter than S_850um>12mJy. We estimate that approximately one-third of these SMG-SMG pairs are physically associated (with a higher rate for the brighter secondary SMGs, S_870um>3mJy), and illustrate this with the serendipitous detection of bright [CII] 157.74um line emission in two SMGs, AS2COS0001.1 & 0001.2 at z=4.63, associated with the highest significance single-dish source. Using our source catalogue we construct the interferometric 870um number counts at S_870um>6.2mJy. We use the extensive archival data of this field to construct the multiwavelength spectral energy distribution of each AS2COSMOS SMG, and subsequently model this emission with MAGPHYS to estimate their photometric redshifts. We find a median photometric redshift for the S_870um>6.2mJy AS2COSMOS sample of z=2.87+/-0.08, and clear evidence for an increase in the median redshift with 870-um flux density suggesting strong evolution in the bright-end of the 870um luminosity function.
We perform lens modelling and source reconstruction of Submillimeter Array (SMA) data for a sample of 12 strongly lensed galaxies selected at 500$mu$m in the Herschel Astrophysical Terahertz Large Area Survey H-ATLAS. A previous analysis of the same dataset used a single S`ersic profile to model the light distribution of each background galaxy. Here we model the source brightness distribution with an adaptive pixel scale scheme, extended to work in the Fourier visibility space of interferometry. We also present new SMA observations for seven other candidate lensed galaxies from the H-ATLAS sample. Our derived lens model parameters are in general consistent with previous findings. However, our estimated magnification factors, ranging from 3 to 10, are lower. The discrepancies are observed in particular where the reconstructed source hints at the presence of multiple knots of emission. We define an effective radius of the reconstructed sources based on the area in the source plane where emission is detected above 5$sigma$. We also fit the reconstructed source surface brightness with an elliptical Gaussian model. We derive a median value $r_{eff},sim 1.77,$kpc and a median Gaussian full width at half maximum $sim1.47,$kpc. After correction for magnification, our sources have intrinsic star formation rates SFR$,sim900-3500,M_{odot}yr^{-1}$, resulting in a median star formation rate surface density $Sigma_{SFR}sim132,M_{odot}$ yr$^{-1}$ kpc$^{-2}$ (or $sim 218,M_{odot}$ yr$^{-1}$ kpc$^{-2}$ for the Gaussian fit). This is consistent with what observed for other star forming galaxies at similar redshifts, and is significantly below the Eddington limit for a radiation pressure regulated starburst.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
