Yun, Min

Job Title

Professor, Department of Astronomy

Last Name

Yun

First Name

Min

Discipline

Astrophysics and Astronomy

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Now showing 1 - 10 of 82

STAR FORMATION RATES IN LYMAN BREAK GALAXIES: RADIO STACKING OF LBGs IN THE COSMOS FIELD AND THE SUB-mu Jy RADIO SOURCE POPULATION
(2008-01) Carilli, CL; Lee, N; Capak, P; Schinnerer, E; Lee, KS; McCraken, H; Yun, Min; Scoville, N; Smolcic, V; Giavalisco, M; Datta, A; Taniguchi, Y; Urry, CM
We present an analysis of the radio properties of large samples of Lyman break galaxies (LBGs) at z ~ 3, 4, and 5 from the COSMOS field. The median stacking analysis yields a statistical detection of the z ~ 3 LBGs (U-band dropouts), with a 1.4 GHz flux density of 0.90 ± 0.21 μJy. The stacked emission is unresolved, with a size <1, or a physical size <8 kpc. The total star formation rate implied by this radio luminosity is 31 ± 7 M yr−1, based on the radio-FIR correlation in low-redshift star-forming galaxies. The star formation rate derived from a similar analysis of the UV luminosities is 17 M yr−1, without any correction for UV dust attenuation. The simplest conclusion is that the dust attenuation factor is 1.8 at UV wavelengths. However, this factor is considerably smaller than the standard attenuation factor of ~5, normally assumed for LBGs. We discuss potential reasons for this discrepancy, including the possibility that the dust attenuation factor at z ≥ 3 is smaller than at lower redshifts. Conversely, the radio luminosity for a given star formation rate may be systematically lower at very high redshift. Two possible causes for a suppressed radio luminosity are (1) increased inverse Compton cooling of the relativistic electron population due to scattering off the increasing CMB at high redshift or (2) cosmic-ray diffusion from systematically smaller galaxies. The radio detections of individual sources are consistent with a radio-loud AGN fraction of 0.3%. One source is identified as a very dusty, extreme starburst galaxy (a "submillimeter galaxy").
A GREEN BANK TELESCOPE SURVEY FOR H I 21 cm ABSORPTION IN THE DISKS AND HALOS OF LOW-REDSHIFT GALAXIES*
(2011-01) Borthakur, S; Tripp, TM; Yun, Min; Bowen, DV; Meiring, JD; York, DG; Momjian, E
We present an H I 21 cm absorption survey with the Green Bank Telescope (GBT) of galaxy-quasar pairs selected by combining galaxy data from the Sloan Digital Sky Survey (SDSS) and radio sources from the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) survey. Our sample consists of 23 sight lines through 15 low-redshift foreground galaxy-background quasar pairs with impact parameters ranging from 1.7 kpc up to 86.7 kpc. We detected one absorber in the GBT survey from the foreground dwarf galaxy, GQ1042+0747, at an impact parameter of 1.7 kpc and another possible absorber in our follow-up Very Large Array (VLA) imaging of the nearby foreground galaxy UGC 7408. The line widths of both absorbers are narrow (FWHM of 3.6 and 4.8km s–1). The absorbers have sub-damped Lyα column densities, and most likely originate in the disk gas of the foreground galaxies. We also detected H I emission from three foreground galaxies including UGC 7408. Although our sample contains both blue and red galaxies, the two H I absorbers as well as the H I emissions are associated with blue galaxies. We discuss the physical conditions in the 21 cm absorbers and some drawbacks of the large GBT beam for this type of survey.
A complete view of galaxy evolution: panchromatic luminosity functions and the generation of metals
(2009-01) Blain, AW; Armus, L; Bertoldi, F; Bock, J; Bradford, M; Dowell, CD; Glenn, J; Goldsmith, P; Harwit, M; Helou, G; Smith, JD; Soifer, BT; Stacey, G; Vieira, J; Yun, Min; Zmuidzinas, J
When and how did galaxies form and their metals accumulate? Over the last decade, this has moved from an archeological question to a live investigation: there is now a broad picture of the evolution of galaxies in dark matter halos: their masses, stars, metals and supermassive blackholes. Galaxies have been found and studied in which these formation processes are taking place most vigorously, all the way back in cosmic time to when the intergalactic medium (IGM) was still largely neutral. However, the details of how and why the interstellar medium (ISM) in distant galaxies cools, is processed, recycled and enriched in metals by stars, and fuels active galactic nuclei (AGNs) remain uncertain. In particular, the cooling of gas to fuel star formation, and the chemistry and physics of the most intensely active regions is hidden from view at optical wavelengths, but can be seen and diagnosed at mid- & far-infrared (IR) wavelengths. Rest-frame IR observations are important first to identify the most luminous, interesting and important galaxies, secondly to quantify accurately their total luminosity, and finally to use spectroscopy to trace the conditions in the molecular and atomic gas out of which stars form. In order to map out these processes over the full range of environments and large-scale structures found in the universe - from the densest clusters of galaxies to the emptiest voids - we require tools for deep, large area surveys, of millions of galaxies out to z~5, and for detailed follow-up spectroscopy. The necessary tools can be realized technically. Here, we outline the requirements for gathering the crucial information to build, validate and challenge models of galaxy evolution.
AzTEC half square degree survey of the SHADES fields - I. Maps, catalogues and source counts
(2010-01) Austermann, JE; Yun, Min
We present the first results from the largest deep extragalactic mm-wavelength survey undertaken to date. These results are derived from maps covering over 0.7 deg2, made at λ= 1.1 mm, using the AzTEC continuum camera mounted on the James Clerk Maxwell Telescope. The maps were made in the two fields originally targeted at λ= 850 μm with the Submillimetre Common-User Bolometer Array (SCUBA) in the SCUBA Half-Degree Extragalactic Survey (SHADES) project, namely the Lockman Hole East (mapped to a depth of 0.9–1.3 mJy rms) and the Subaru/XMM–Newton Deep Field (mapped to a depth of 1.0–1.7 mJy rms). The wealth of existing and forthcoming deep multifrequency data in these two fields will allow the bright mm source population revealed by these new wide-area 1.1 mm images to be explored in detail in subsequent papers. Here, we present the maps themselves, a catalogue of 114 high-significance submillimetre galaxy detections, and a thorough statistical analysis leading to the most robust determination to date of the 1.1 mm source number counts. These new maps, covering an area nearly three times greater than the SCUBA SHADES maps, currently provide the largest sample of cosmological volumes of the high-redshift Universe in the mm or sub-mm. Through careful comparison, we find that both the Cosmic Evolution Survey (COSMOS) and the Great Observatories Origins Deep Survey (GOODS) North fields, also imaged with AzTEC, contain an excess of mm sources over the new 1.1 mm source-count baseline established here. In particular, our new AzTEC/SHADES results indicate that very luminous high-redshift dust enshrouded starbursts (S1.1mm > 3 mJy) are 25–50 per cent less common than would have been inferred from these smaller surveys, thus highlighting the potential roles of cosmic variance and clustering in such measurements. We compare number count predictions from recent models of the evolving mm/sub-mm source population to these sub-mm bright galaxy surveys, which provide important constraints for the ongoing refinement of semi-analytic and hydrodynamical models of galaxy formation, and find that all available models overpredict the number of bright submillimetre galaxies found in this survey.
(CO)-C-12(J=1-0) ON-THE-FLY MAPPING SURVEY OF THE VIRGO CLUSTER SPIRALS. I. DATA AND ATLAS
(2009-01) Chung, E.J.; Rhee, M.-H.; Kim, H.; Yun, Min S.; Heyer, M.; Young, J. S.
We have performed an On-The-Fly (OTF) mapping survey of 12CO(J = 1-0) emission in 28 Virgo cluster spiral galaxies using the Five College Radio Astronomy Observatory (FCRAO) 14 m telescope. This survey aims to characterize the CO distribution, kinematics, and luminosity of a large sample of galaxies covering the full extents of stellar disks, rather than sampling only the inner disks or the major axis as was done by many previous single dish and interferometric CO surveys. CO emission is detected in 20 galaxies among the 28 Virgo spirals observed. An atlas consisting of global measures, radial measures, and maps is presented for each detected galaxy. A note summarizing the CO data is also presented along with relevant information from the literature. The CO properties derived from our OTF observations are presented and compared with the results from the FCRAO Extragalactic CO Survey by Young et al. which utilized position-switching observations along the major axis and a model fitting method. We find that our OTF-derived CO properties agree well with the Young et al. results in many cases, but the Young et al. measurements are larger by a factor of 1.4-2.4 for seven (out of 18) cases. We will explore further the possible causes for the discrepancy in the analysis paper currently under preparation.
DETECTION OF DIFFUSE NEUTRAL INTRAGROUP MEDIUM IN HICKSON COMPACT GROUPS
(2010-01) Borthakur, S; Yun, Min; Verdes-Montenegro, L
We present new Green Bank Telescope (GBT) 21 cm neutral hydrogen (H I) observations of a complete distance-limited sample of 22 Hickson Compact Groups (HCGs) with at least four true members. We detected an average H I mass of 8 × 109 M (median = 6 × 109 M ), which is significantly larger than previous single-dish measurements. Consequently, the H I deficiencies for these HCGs have been reduced, although not completely eliminated. Spectral comparison of the GBT data with complementary Very Large Array data shows significant H I excess in the GBT spectra. The observed excess is primarily due to the high surface brightness (HSB) sensitivity of the GBT detecting diffuse, low column density H I in these groups. The excess gas forms a faint diffused neutral medium which is an intermediate stage in the evolution of HSB H I tidal debris in the intragroup medium (IGM) before it is fully ionized. The excess gas mass fraction, (M(H I)GBT – M(H I)VLA)/M(H I)GBT, for our complete sample varies from 5% to 81% with an average of 36% (median = 30%). The excess gas mass fraction is highest in slightly H I deficient groups where the tidal debris has had enough time to evolve. We also find the excess gas content increases with the evolutionary phase of the group described in Verdes-Montenegro et al. Theoretical calculations indicate that an H I cloud of radius ≥ 200 pc would survive in an IGM of 2 × 106 K for more than the typical dynamical lifetime of a group. However, smaller clouds get evaporated and assimilated into the hot IGM in a much shorter timescale.
The Evolution of Galaxy Disks in Dense Environments - Lessons from Compact Galaxy Groups
(2008-01) Rasmussen, J; Ponman, TJ; Verdes-Montenegro, L; Yun, Min; Borthakur, S
Disk galaxies in compact galaxy groups exhibit a remarkable shortfall of neutral hydrogen compared to both isolated spirals and spirals in more loose groups, but the origin of this HI deficiency remains unclear. Based on a sample of highly HI deficient compact galaxy groups, here updated to also include HCG 58 and HCG 93, we summarise the first results of a multi-wavelength campaign aimed at understanding the processes responsible for modifying the HI content of galaxy disks in these environments. While tidal stripping, ram pressure stripping by hot intragroup gas, and star-formation induced strangulation could individually be affecting the ISM in some of the group members, these processes each face specific difficulties in explaining the inferred deficiency of HI for the sample as a whole. A complete picture of the mechanisms driving the ISM evolution in the disk galaxies of these groups has thus yet to emerge, but promising avenues for further progress in this field are briefly discussed on the basis of the present sample.
MID-INFRARED SPECTROSCOPY OF CANDIDATE ACTIVE GALACTIC NUCLEI-DOMINATED SUBMILLIMETER GALAXIES
(2008-01) Schinnerer, E; Carilli, CL; Capak, P; Martinez-Sansigre, A; Scoville, NZ; Smolcic, V; Taniguchi, Y; Yun, Min; Bertoldi, F; Fe Fevre, O; de Ravel, L
We report the detection of CO molecular line emission in the z = 4.5 millimeter-detected galaxy COSMOS J100054+023436 (hereafter J1000+0234) using the IRAM Plateau de Bure interferometer (PdBI) and NRAO's Very Large Array (VLA). The 12CO(4-3) line as observed with PdBI has a full line width of ~1000 km s−1, an integrated line flux of 0.66 Jy km s−1, and a CO luminosity of 3.2 × 1010 L. Comparison to the 3.3 σ detection of the CO(2-1) line emission with the VLA suggests that the molecular gas is likely thermalized to the J = 4–3 transition level. The corresponding molecular gas mass is 2.6 × 1010 M assuming an ULIRG-like conversion factor. From the spatial offset of the red- and blueshifted line peaks and the line width a dynamical mass of 1.1 × 1011 M is estimated assuming a merging scenario. The molecular gas distribution coincides with the rest-frame optical and radio position of the object while being offset by 0.5'' from the previously detected Lyα emission. J1000+0234 exhibits very typical properties for lower redshift (z ~ 2) submillimeter galaxies (SMGs) and thus is very likely one of the long sought after high-redshift (z > 4) objects of this population. The large CO(4-3) line width taken together with its highly disturbed rest-frame UV geometry suggest an ongoing major merger about a billion years after the big bang. Given its large star formation rate (SFR) of >1000 M yr−1 and molecular gas content this object could be the precursor of a "red and dead" elliptical observed at a redshift of z = 2.
MID-INFRARED SPECTROSCOPY OF CANDIDATE ACTIVE GALACTIC NUCLEI-DOMINATED SUBMILLIMETER GALAXIES
(2010-01) Coppin, K; Pope, A; Menendez-Delmestre, K; Alexander, DM; Dunlop, JS; Egami, E; Gabor, J; Ibar, E; Ivison, RJ; Austermann, JE; Blain, AW; Chapman, SC; Clements, DL; Dunne, L; Dye, S; Farrah, D; Hughes, DH; Mortier, AMJ; Page, MJ; Rowan-Robinson, M; Scott, D; Simpson, C; Smail, I; Swinbank, AM; Vaccari, M; Yun, Min
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 (AGNs). We have obtained Spitzer-InfraRed Spectrograph spectroscopy of a sample of eight SMGs that are candidates for harboring powerful AGNs on the basis of IRAC color selection (S 8 μm/S 4.5 μm>2, i.e., likely power-law mid-infrared spectral energy distributions). SMGs with an AGN dominating (50%) their mid-infrared emission could represent the "missing link" sources in an evolutionary sequence involving a major merger. First of all, we detect polycyclic aromatic hydrocarbon (PAH) features in all of the SMGs, indicating redshifts from 2.5 to 3.4, demonstrating the power of the mid-infrared to determine redshifts for these optically faint dusty galaxies. Second, 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 AGNs dominate the bolometric emission of the SMG when the results are extrapolated to longer infrared wavelengths, implying that AGNs 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 S 8 μm/S 4.5 μm>1.65 works well at selecting mid-infrared energetically dominant AGNs 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.
Powerful High-Velocity Dispersion Molecular Hydrogen Associated with an Intergalactic Shock Wave in Stephan's Quintet
(2006-01) Appleton, PN; Xu, KC; Reach, W; Dopita, MA; Gao, Y; Lu, N; Popescu, CC; Sulentic, JW; Tuffs, RJ; Yun, Min
We present the discovery of strong mid-infrared emission lines of molecular hydrogen of apparently high-velocity dispersion (~870 km s-1) originating from a group-wide shock wave in Stephan's Quintet. These Spitzer Space Telescope observations reveal emission lines of molecular hydrogen and little else. This is the first time an almost pure H2 line spectrum has been seen in an extragalactic object. Along with the absence of PAH-dust features and very low excitation ionized gas tracers, the spectra resemble shocked gas seen in Galactic supernova remnants, but on a vast scale. The molecular emission extends over 24 kpc along the X-ray-emitting shock front, but it has 10 times the surface luminosity as the soft X-rays and about one-third the surface luminosity of the IR continuum. We suggest that the powerful H2 emission is generated by the shock wave caused when a high-velocity intruder galaxy collides with filaments of gas in the galaxy group. Our observations suggest a close connection between galaxy-scale shock waves and strong broad H2 emission lines, like those seen in the spectra of ultraluminous infrared galaxies where high-speed collisions between galaxy disks are common.