arXiv subjects

H. S. Hwang

Publications and source records attributed to H. S. Hwang.

43 records · Page 3Linked to original sources

arXiv2011

GOODS-HERSCHEL: evidence for a UV extinction bump in galaxies at z > 1

Dust attenuation curves in external galaxies are useful to study their dust properties as well as to interpret their intrinsic spectral energy distributions. In particular the presence or absence of a UV bump at 2175 A remains an open issue which has consequences on the interpretation of broad band colours of distant galaxies. We study the dust attenuation curve in the UV range at z >1. In particular we search for the presence of a UV bump. We use deep photometric data of the CDFS obtained with intermediate and broad band filters by the MUSYC project to sample the UV rest-frame of galaxies with 1<z <2. Herschel/PACS and Spitzer/MIPS data are used to measure the dust emission. 30 galaxies were selected with high S/N in all bands. Their SEDs from the UV to the far-IR are fitted using the CIGALE code and the characteristics of the dust attenuation curve are obtained. The mean dust attenuation curve we derive exhibits a UV bump at 2175A whose amplitude corresponds to 35 % (76%) that of the MW (LMC2 supershell) extinction curve. An analytical expression of the average attenuation curve is given, it is found slightly steeper than the Calzetti et al. one, although at a 1 sigma level. Our galaxy sample is used to study the derivation of the slopes of the UV continuum from broad band colours, including the GALEX FUV-NUV colour. Systematic errors induced by the presence of the bump are quantified. We compare dust attenuation factors measured with CIGALE to the slope of the UV continuum and find that there is a large scatter around the relation valid for local starbursts (0.7 mag). The uncertainties on the determination of the UV slope lead to an extra systematic error of the order of 0.3 to 0.7 mag on dust attenuation when a filter overlaps the UV bump.

astro-ph.CO↗

arXiv2011

HerMES: Lyman Break Galaxies individually detected at 0.7 < z < 2.0 in GOODS-N with Herschel/SPIRE

As part of the Herschel Multi-tiered Extragalactic Survey we have investigated the rest-frame far-infrared (FIR) properties of a sample of more than 4800 Lyman Break Galaxies (LBGs) in the Great Observatories Origins Deep Survey North field. Most LBGs are not detected individually, but we do detect a sub-sample of 12 objects at 0.7 < z < 1.6 and one object at z ~ 2.0. The ones detected by Herschel SPIRE have redder observed NUV-U and U-R colors than the others, while the undetected ones have colors consistent with average LBGs at z > 2.5. The UV-to-FIR spectral energy distributions of the objects detected in the rest-frame FIR are investigated using the code CIGALE to estimate physical parameters. We find that LBGs detected by SPIRE are high mass, luminous infrared galaxies. It appears that LBGs are located in a triangle-shaped region in the A_FUV vs. Log L_FUV diagram limited by A_FUV=0 at the bottom and by a diagonal following the temporal evolution of the most massive galaxies from the bottom-right to the top-left of the diagram. This upper envelop can be used as upper limits for the UV dust attenuation as a function of L_FUV}. The limits of this region are well explained using a closed-box model, where the chemical evolution of galaxies produces metals, which in turn lead to higher dust attenuation when the galaxies age.

astro-ph.CO↗

arXiv2011

Towards a complete census of high-z ULIRGs with Herschel

Using Herschel PACS and SPIRE observations as part of the HerMES, we explore the far-IR properties of a sample of mid-IR selected starburst dominated ultra-luminous infrared galaxies (ULIRGs) at z ~ 2. We derive robust estimates of infrared luminosities (L_IR) and dust temperatures (Td) of the population and find that galaxies in our sample range from those that are as cold as high-z sub-millimeter galaxies (SMGs) to those that are as warm as optically faint radio galaxies (OFRGs) and local ULIRGs. We also demonstrate that a significant fraction of our sample would be missed from ground based (sub)mm surveys (850-1200μm) showing that the latter introduce a bias towards the detection of colder sources. Similarly, based on PACS data as part of the PEP project, we construct for the first time the full average SED of a sub-sample of infrared luminous Lyman break galaxies at z ~ 3, and find them to have higher T_d when compared to that of SMGs with comparable L_IR. We conclude that high-z ULIRGs span a wide range of dust temperatures, larger than that seen in local ULIRGs, and that Herschel data provide the means to characterize the bulk of the ULIRG population, free from selection biases introduced by ground based (sub)mm surveys.

astro-ph.CO↗

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

A First Glimpse into the far-IR properties of high-z UV-selected Galaxies: Herschel/PACS observations of z~3 LBGs

We present first insights into the far-IR properties for a sample of IRAC and MIPS-24um detected Lyman Break Galaxies (LBGs) at z ~ 3, as derived from observations in the northern field of the Great Observatories Origins Survey (GOODS-N) carried out with the PACS instrument on board the Herschel Space Observatory. Although none of our galaxies are detected by Herschel, we employ a stacking technique to construct, for the first time, the average spectral energy distribution of infrared luminous LBGs from UV to radio wavelengths. We derive a median IR luminosity of L_{IR} = 1.6 x 10^12 Lo, placing the population in the class of ultra luminous infrared galaxies (ULIRGs). Complementing our study with existing multi-wavelength data, we put constraints on the dust temperature of the population and find that for their L_{IR}, MIPS-LBGs are warmer than submm-luminous galaxies while they fall in the locus of the L_{IR}-T_{d} relation of the local ULIRGs. This, along with estimates based on the average SED, explains the marginal detection of LBGs in current sub-mm surveys and suggests that these latter studies introduce a bias towards the detection of colder ULIRGs in the high-z universe, while missing high-z ULIRGS with warmer dust.

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arXiv2010

Unveiling Far-Infrared Counterparts of Bright Submillimeter Galaxies Using PACS Imaging

We present a search for Herschel-PACS counterparts of dust-obscured, high-redshift objects previously selected at submillimeter and millimeter wavelengths in the Great Observatories Origins Deep Survey North field. We detect 22 of 56 submillimeter galaxies (39%) with a SNR of >=3 at 100 micron down to 3.0 mJy, and/or at 160 micron down to 5.7 mJy. The fraction of SMGs seen at 160 micron is higher than that at 100 micron. About 50% of radio-identified SMGs are associated with PACS sources. We find a trend between the SCUBA/PACS flux ratio and redshift, suggesting that these flux ratios could be used as a coarse redshift indicator. PACS undetected submm/mm selected sources tend to lie at higher redshifts than the PACS detected ones. A total of 12 sources (21% of our SMG sample) remain unidentified and the fact that they are blank fields at Herschel-PACS and VLA 20 cm wavelength may imply higher redshifts for them than for the average SMG population (e.g., z>3-4). The Herschel-PACS imaging of these dust-obscured starbursts at high-redshifts suggests that their far-infrared spectral energy distributions have significantly different shapes than template libraries of local infrared galaxies.

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.

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