arXiv subjects

Min S. Yun

Publications and source records attributed to Min S. Yun.

At least 109 records · Page 6Linked to original sources

arXiv2011

Deep 1.1 mm-wavelength imaging of the GOODS-South field by AzTEC/ASTE -- II. Redshift distribution and nature of the submillimetre galaxy population

We report the results of the counterpart identification and a detailed analysis of the physical properties of the 48 sources discovered in our deep 1.1mm wavelength imaging survey of the GOODS-South field using the AzTEC instrument on the Atacama Submillimeter Telescope Experiment (ASTE). One or more robust or tentative counterpart candidate is found for 27 and 14 AzTEC sources, respectively, by employing deep radio continuum, Spitzer MIPS & IRAC, and LABOCA 870 micron data. Five of the sources (10%) have two robust counterparts each, supporting the idea that these galaxies are strongly clustered and/or heavily confused. Photometric redshifts and star formation rates (SFRs) are derived by analyzing UV-to-optical and IR-to-radio SEDs. The median redshift of z~2.6 is similar to other earlier estimates, but we show that 80% of the AzTEC-GOODS sources are at z>2, with a significant high redshift tail (20% at z>3.3). Rest-frame UV and optical properties of AzTEC sources are extremely diverse, spanning 10 magnitude in the i- and K-band photometry with median values of i=25.3 and K=22.6 and a broad range of red colour (i-K=0-6). These AzTEC sources are some of the most luminous galaxies in the rest-frame optical bands at z>2, with inferred stellar masses of (1-30) x 10^{10} solar masses and UV-derived star formation rates of SFR(UV) > 10-1000 solar masses per year. The IR-derived SFR, 200-2000 solar masses per year, is independent of redshift or stellar mass. The resulting specific star formation rates, SSFR = 1-100 per Gyr, are 10-100 times higher than similar mass galaxies at z=0, and they extend the previously observed rapid rise in the SSFR with redshift to z=2-5. These galaxies have a SFR high enough to have built up their entire stellar mass within their Hubble time. We find only marginal evidence for an AGN contribution to the near-IR and mid-IR SEDs. (abridged)

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arXiv2011

Evidence for 1000 km/s Molecular Outflows in the Local ULIRG Population

The feedback from galactic outflows is thought to play an important role in shaping the gas content, star formation history, and ultimately the stellar mass function of galaxies. Here we present evidence for massive molecular outflows associated with ultra-luminous infrared galaxies (ULIRGs) in the coadded Redshift Search Receiver 12CO(1-0) spectrum. Our stacked spectrum of 27 ULIRGs at z = 0.043-0.11 (freq_rest = 110-120 GHz) shows broad wings around the CO line with delta_V(FWZI)~2000 km/s. Its integrated line flux accounts for up to 25+/-5% of the total CO line luminosity. When interpreted as a massive molecular outflow wind, the associated mechanical energy can be explained by a concentrated starburst with SFR \geq 100 M_sun/yr, which agrees well with their SFR derived from the FIR luminosity. Using the high signal-to-noise stacked composite spectrum, we also probe 13CO and 12CN emission in the sample and discuss how the chemical abundance of molecular gas may vary depending on the physical conditions of the nuclear region.

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arXiv2011

On the Clustering of Sub-millimeter Galaxies

We measure the angular two-point correlation function of sub-millimeter galaxies (SMGs) from 1.1-millimeter imaging of the COSMOS field with the AzTEC camera and ASTE 10-meter telescope. These data yields one of the largest contiguous samples of SMGs to date, covering an area of 0.72 degrees^2 down to a 1.26 mJy/beam (1-sigma) limit, including 189 (328) sources with S/N greater than 3.5 (3). We can only set upper limits to the correlation length r_0, modeling the correlation function as a power-law with pre-assigned slope. Assuming existing redshift distributions, we derive 68.3% confidence level upper limits of r_0 < 6-8 h^-1 Mpc at 3.7 mJy, and r_0 < 11-12 h^-1 Mpc at 4.2 mJy. Although consistent with most previous estimates, these upper limits imply that the real r_0 is likely smaller. This casts doubts on the robustness of claims that SMGs are characterized by significantly stronger spatial clustering, (and thus larger mass), than differently selected galaxies at high-redshift. Using Monte Carlo simulations we show that even strongly clustered distributions of galaxies can appear unclustered when sampled with limited sensitivity and coarse angular resolution common to current sub-millimeter surveys. The simulations, however, also show that unclustered distributions can appear strongly clustered under these circumstances. From the simulations, we predict that at our survey depth, a mapped area of two degrees^2 is needed to reconstruct the correlation function, assuming smaller beam sizes of future surveys (e.g. the Large Millimeter Telescope's 6" beam size). At present, robust measures of the clustering strength of bright SMGs appear to be below the reach of most observations.

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arXiv2011

IRAS 15099-5856: Remarkable Mid-Infrared Source with Prominent Crystalline Silicate Emission Embedded in the Supernova Remnant MSH15-52

We report new mid-infrared observations of the remarkable object IRAS 15099-5856 using the space telescopes AKARI and Spitzer, which demonstrate the presence of prominent crystalline silicate emission in this bright source. IRAS 15099-5856 has a complex morphology with a bright central compact source (IRS1) surrounded by knots, spurs, and several extended (~4') arc-like filaments. The source is seen only at >= 10 um. The Spitzer MIR spectrum of IRS1 shows prominent emission features from Mg-rich crystalline silicates, strong [Ne II] 12.81 um and several other faint ionic lines. We model the MIR spectrum as thermal emission from dust and compare with the Herbig Be star HD 100546 and the luminous blue variable R71, which show very similar MIR spectra. Molecular line observations reveal two molecular clouds around the source, but no associated dense molecular cores. We suggest that IRS1 is heated by UV radiation from the adjacent O star Muzzio 10 and that its crystalline silicates most likely originated in a mass outflow from the progenitor of the supernova remnant (SNR) MSH 15-52. IRS1, which is embedded in the SNR, could have been shielded from the SN blast wave if the progenitor was in a close binary system with Muzzio 10. If MSH15-52 is a remnant of Type Ib/c supernova (SN Ib/c), as has been previously proposed, this would confirm the binary model for SN Ib/c. IRS1 and the associated structures may be the relics of massive star death, as shaped by the supernova explosion, the pulsar wind and the intense ionizing radiation of the embedded O star.

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arXiv2011

Identification of a Complete 160 micron Flux-Limited Sample of Infrared Galaxies in the ISO Lockman Hole 1-Deg^2 Deep Fields: Source Properties and Evidence for Strong Evolution in the FIR Luminosity Function for ULIRGs

We have identified a complete, flux-limited, (S_160>120 mJy), sample of 160 micron-selected sources from Spitzer observations of the 1-deg^2 ISO Deep Field region in the Lockman Hole. Ground-based UV, optical and near-infrared (NIR) photometry and optical spectroscopy have been used to determine colors, redshifts and masses for the complete sample of 40 galaxies. Spitzer-IRAC+MIPS photometry, supplemented by ISOPHOT data at 90 micron and 170 micron, has been used to calculate accurate total infrared luminosities, LIR(8-1000 micron), and to determine the IR luminosity function (LF) of luminous infrared galaxies (LIRGs). The maximum observed redshift is z~0.80 and the maximum total infrared luminosity is log(L_IR/L_Sun)=12.74. Over the luminosity range log(L_IR/L_Sun)=10-12, the LF for LIRGs in the Lockman Hole Deep Field is similar to that found previously for local sources at similar infrared luminosities. The mean host galaxy mass, log(M/M_Sun)=10.7, and dominance of HII-region spectral types, is also similar to what has been found for local LIRGs, suggesting that intense starbursts likely power the bulk of the infrared luminosity for sources in this range of LIR. However for the most luminous sources, log(L_IR/L_Sun)>12.0, we find evidence for strong evolution in the LF \propto (1+z)6\pm1, assuming pure number density evolution. These ultraluminous infrared galaxies (ULIRGs) have a larger mean host mass, log(M/M_Sun)=11.0, and exhibit disturbed morphologies consistent with strong-interactions/mergers, and they are also more likely to be characterized by starburst-AGN composite or AGN spectral types.

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arXiv2010

The Redshift Search Receiver 3 mm Wavelength Spectra of 10 Galaxies

The 3 mm wavelength spectra of 10 galaxies have been obtained at the Five College Radio Astronomy Observatory using a new, very broadband receiver and spectrometer, called the Redshift Search Receiver (RSR). The RSR has an instantaneous bandwidth of 37 GHz covering frequencies from 74 to 111 GHz, and has a spectral resolution of 31 MHz (~100 km/s). During tests of the RSR on the FCRAO 14 m telescope the complete 3 mm spectra of the central regions of NGC 253, Maffei 2, NGC1068, IC 342, M82, NGC 3079, NGC 3690, NGC 4258, Arp 220 and NGC 6240 were obtained. Within the wavelength band covered by the RSR, 20 spectral lines from 14 different atomic and molecular species were detected. Based on simultaneous fits to the spectrum of each galaxy, a number of key molecular line ratios are derived. A simple model which assumes the emission arises from an ensemble of Milky Way-like Giant Nolecular Cloud cores can adequately fit the observed line ratios using molecular abundances based on Galactic molecular cloud cores. Variations seen in some line ratios, such as 13CO/HCN and HCO+/HCN, can be explained if the mean density of the molecular gas varies from galaxy to galaxy. However, NGC 3690, NGC 4258 and NGC 6240 show very large HCO+/HCN ratios and require significant abundance enhancement of HCO+ over HCN, possible due to the proximity to active galactic nucleus activity. Finally, the mass of dense molecular gas is estimated and we infer that 25-85 % of the total molecular gas in the central regions of these galaxies must have densities greater than 10^4 cm^-3.

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arXiv2010

Detection of Strong Millimeter Emission from the Circumstellar Dust Disk Around V1094 Sco: Cold and Massive Disk around a T Tauri Star in a Quiescent Accretion Phase?

We present the discovery of a cold massive dust disk around the T Tauri star V1094 Sco in the Lupus molecular cloud from the 1.1 millimeter continuum observations with AzTEC on ASTE. A compact ($r\lesssim$320 AU) continuum emission coincides with the stellar position having a flux density of 272 mJy which is largest among T Tauri stars in Lupus. We also present the detection of molecular gas associated with the star in the five-point observations in $^{12}$CO J=3--2 and $^{13}$CO J=3--2. Since our $^{12}$CO and $^{13}$CO observations did not show any signature of a large-scale outflow or a massive envelope, the compact dust emission is likely to come from a disk around the star. The observed SED of V1094 Sco shows no distinct turnover from near infrared to millimeter wavelengths, which can be well described by a flattened disk for the dust component, and no clear dip feature around 10 $\micron$ suggestive of absence of an inner hole in the disk. We fit a simple power-law disk model to the observed SED. The estimated disk mass ranges from 0.03 to $\gtrsim$0.12 $M_\sun$, which is one or two orders of magnitude larger than the median disk mass of T Tauri stars in Taurus.

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arXiv2010

A GBT Survey for HI 21 cm Absorption in the Disks and Halos of Low-Redshift Galaxies

We present an HI 21 cm absorption survey with the Green Bank Telescope (GBT) of galaxy-quasar pairs selected by combining data from the Sloan Digital Sky Survey (SDSS) and the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) survey. Our sample consists of 23 sightlines 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. Both of the absorbers are narrow (FWHM of 3.6 and 4.8 km/s), have sub Damped Lyman alpha 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.

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arXiv2010

Using 21cm Absorption in Small Impact Parameter Galaxy-QSO Pairs to Probe Low-Redshift Damped and Sub-Damped Lyman-alpha System

To search for low-redshift damped Lyman-alpha (DLA) and sub-DLA quasar absorbers, we have conducted a 21cm absorption survey of radio-loud quasars at small impact parameters to foreground galaxies selected from the Sloan Digital Sky Survey (SDSS). Here we present the first results from this survey based on observations of SDSS J104257.58+074850.5 ($z_{QSO}$ = 2.66521), a quasar at an angular separation from a foreground galaxy ($z_{gal}$ = 0.03321) of 2.5" (1.7 kpc in projection). The foreground galaxy is a low-luminosity spiral with on-going star formation (0.004 M$_{\odot}$ yr$^{-1}$ kpc$^{-2}$) and a metallicity of $-0.27 \pm 0.05$ dex. We detect 21cm absorption from the galaxy with the Green Bank Telescope (GBT), the Very Large Array (VLA), and the Very Long Baseline Array (VLBA). The absorption appears to be quiescent disk gas corotating with the galaxy and we do not find any evidence for outflowing cold neutral gas. The width of the main absorption line indicates that the gas is cold, $T_{k} < 283$ K, and the HI column is surprisingly low given the impact parameter of 1.7 kpc; we find that N(HI) $\leq 9.6 \times 10^{19}$ cm$^{-2}$ (GBT) and N(HI) $\leq 1.5 \times 10^{20}$ cm$^{-2}$ (VLBA). VLBA marginally resolves the continuum source and the absorber, and a lower limit of 27.1 $\times$ 13.9 pc is derived for the size of the absorbing cloud. In turn, this indicates a low density for a cold cloud, n(HI) $<$ 3.5 cm$^{-3}$. We hypothesize that this galaxy, which is relatively isolated, is becoming depleted in HI because it is converting its interstellar matter into stars without a replenishing source of gas, and we suggest future observations to probe this and similar galaxies.

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arXiv2010

Color Magnitude Relation and Morphology of Low-Redshift ULIRGs in SDSS

We present color-magnitude and morphological analysis of 54 low-redshift ULIRGs, a subset of the IRAS 1Jy sample (Kim & Sanders, 1998), in the SDSS. The ULIRGs are on average 1 magnitude brighter in M0.1r than the SDSS galaxies within the same redshift range. The majority of the ULIRGs (~87%) have the colors typical of the blue cloud, and only 4 sources (~7%) are located in the red sequence. While ULIRGs are popularly thought to be precursors to a QSO phase, we find few (~6%) in the "green valley" where the majority of the X-ray and IR selected AGNs are found, and none of which harbors an AGN. For the 14 previously spectroscopic identified AGNs (~28%), we perform PSF subtractions and find that on average the central point sources contribute less than one third to the total luminosity, and that their high optical luminosities and overall blue colors are apparently the result of star formation activity of the host galaxies. Visual inspection of the SDSS images reveals a wide range of disturbed morphologies. A detailed morphology analysis using Gini and M20 coefficients shows that slightly less than one half (~42% in g band) of the ULIRGs are located in the region where most local mergers are found. The heterogeneous distribution of ULIRGs in the G-M20 space is qualitatively consistent with the results found by numerical simulations of disk-disk mergers. Our study also shows that the measured morphological parameters are systematically affected by the SNR and thus the merging galaxies can appear at various regions in the G-M20 space. In general, our results reinforce the view that ULIRGs contain young stellar populations and are mergers in progress. Our study provides a uniform comparison sample for studying ULIRGs at higher redshifts such as Spitzer mid-IR selected ULIRGs at z=1~2 and submm galaxies.

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arXiv2010

An Investigation of the Dust Content in the Galaxy pair NGC 1512/1510 from Near-Infrared to Millimeter Wavelengths

We combine new ASTE/AzTEC 1.1 mm maps of the galaxy pair NGC 1512/1510 with archival Spitzer IRAC and MIPS images covering the wavelength range 3.6--160 um from the SINGS project to derive accurate dust masses in each galaxy, and in sub--galactic regions in NGC 1512. The two galaxies form a pair consisting of a large, high--metallicity spiral (NGC 1512) and a low metallicity, blue compact dwarf (NGC 1510). The derived total dust masses are (2.4+/-0.6) 10^7 Msun and (1.7+/-3.6) 10^5 Msun for NGC 1512 and NGC 1510, respectively. The derived ratio of dust mass to H I gas mass for the galaxy pair (0.0034) is much lower than expected, while regions within NGC 1512, specifically the central region and the arms, do not show such unusually low ratios; furthermore, the dust--to--gas ratio is within expectations for NGC 1510. These results suggest that a fraction of the H I included in the determination of the M_d/M_HI ratio of the NGC 1512/1510 pair is not associated with the star forming disks/regions of either galaxy. We also perform simple two--temperature (warm + cold) modified--blackbody fits to the far--infrared/mm data. The warm dust temperature of the low--metallicity NGC 1510 (~36 K) is substantially higher than that of the high--metallicity NGC 1512 (~24 K). In both galaxies, a substantial fraction (>93%) of the total dust mass is in a cool dust component, with temperatures 14--16 K for NGC 1512 and 15--24 K for NGC 1510. In contrast, the warm dust in the arms and central regions of NGC 1512 represents a much larger fraction of the total dust content, in agreement with the fact that all three regions have higher specific star formation rates than the average in the galaxy.

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arXiv2009

The Redshift Search Receiver Observations of 12CO J=1-->0 in 29 Ultraluminous Infrared Galaxies

We present 12CO J=1-->0 observations of ultraluminous infrared galaxies (ULIRGs) obtained using the Redshift Search Receiver (RSR) on the 14-m telescope of the Five College Radio Astronomy Observatory. The RSR is a novel, dual-beam, dual-polarization receiver equipped with an ultra-wideband spectrometer backend that is being built as a facility receiver for the Large Millimeter Telescope. Our sample consists of 29 ULIRGs in the redshift range of 0.04-0.11, including 10 objects with no prior 12CO measurements. We have detected 27 systems (a detection rate of 93%), including 9 ULIRGs that are detected in CO for the first time. Our study has increased the number of local ULIRGs with CO measurements by ~15%. The CO line luminosity L'_CO, correlates well with far-infrared luminosity L_FIR, following the general trend of other local ULIRGs. However, compared to previous surveys we probe deeper into the low CO luminosity end of ULIRG population as a single study by including a number of CO faint objects in the sample. As a result, we find 1) a smoother transition between the ULIRG population and local QSOs in L_FIR-L'_CO ("star formation efficiency") space, and 2) a broader range of L_FIR/L'_CO flux ratio (~60--1000 L_sun/[K km/s/pc^2]) than previously reported. In our new survey, we also have found a small number of ULIRGs with extreme L_FIR/L'_CO which had been known to be rare. The mid-IR color and radio-excess of 56 local ULIRGs as a function of FIR-to-CO flux ratio is examined and compared with those of spirals/starburst galaxies and low-z QSOs. In this paper, using a large sample of local ULIRGs we explore the origin of their current power source and potential evolution to QSOs.

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arXiv2009

Spatial correlation between submillimetre and Lyman-alpha galaxies in the SSA 22 protocluster

Lyman-alpha emitters are thought to be young, low-mass galaxies with ages of ~10^8 yr. An overdensity of them in one region of the sky (the SSA 22 field) traces out a filamentary structure in the early Universe at a redshift of z = 3.1 (equivalent to 15 per cent of the age of the Universe) and is believed to mark a forming protocluster. Galaxies that are bright at (sub)millimetre wavelengths are undergoing violent episodes of star formation, and there is evidence that they are preferentially associated with high-redshift radio galaxies, so the question of whether they are also associated with the most significant large-scale structure growing at high redshift (as outlined by Lyman-alpha emitters) naturally arises. Here we report an imaging survey of 1,100-um emission in the SSA 22 region. We find an enhancement of submillimetre galaxies near the core of the protocluster, and a large-scale correlation between the submillimetre galaxies and the low-mass Lyman-alpha emitters, suggesting synchronous formation of the two very different types of star-forming galaxy within the same structure at high redshift. These results are in general agreement with our understanding of the formation of cosmic structure.

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arXiv2009

Luminous Infrared Galaxies with the Submillimeter Array: II. Comparing the CO(3-2) Sizes and Luminosities of Local and High-Redshift Luminous Infrared Galaxies

We present a detailed comparison of the CO(3-2) emitting molecular gas between a local sample of luminous infrared galaxies (U/LIRGs) and a high redshift sample that comprises submm selected galaxies (SMGs), quasars, and Lyman Break Galaxies (LBGs). The U/LIRG sample consists of our recent CO(3-2) survey using the Submillimeter Array while the CO(3-2) data for the high redshift population are obtained from the literature. We find that the L(CO(3-2)) and L(FIR) relation is correlated over five orders of magnitude, which suggests that the molecular gas traced in CO(3-2) emission is a robust tracer of dusty star formation activity. The near unity slope of 0.93 +/- 0.03 obtained from a fit to this relation suggests that the star formation efficiency is constant to within a factor of two across different types of galaxies residing in vastly different epochs. The CO(3-2) size measurements suggest that the molecular gas disks in local U/LIRGs (0.3 - 3.1 kpc) are much more compact than the SMGs (3 - 16 kpc), and that the size scales of SMGs are comparable to the nuclear separation (5 - 40 kpc) of the widely separated nuclei of U/LIRGs in our sample. We argue from these results that the SMGs studied here are predominantly intermediate stage mergers, and that the wider line-widths arise from the violent merger of two massive gas-rich galaxies taking place deep in a massive halo potential.

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arXiv2008

The Physical Scale of the Far-Infrared Emission in the Most Luminous Submillimeter Galaxies

We present high resolution submillimeter interferometric imaging of two of the brightest high-redshift submillimeter galaxies known: GN20 and AzTEC1 at 0.8 and 0.3 arcsec resolution respectively. Our data - the highest resolution submillimeter imaging of high redshift sources accomplished to date - was collected in three different array configurations: compact, extended, and very extended. We derive angular sizes of 0.6 and 1.0 arcsec for GN20 and 0.3 and 0.4 arcsec for AzTEC1 from modeling their visibility functions as a Gaussian and elliptical disk respectively. Because both sources are B-band dropouts, they likely lie within a relatively narrow redshift window around z~4, which indicates their angular extent corresponds to physical scales of 4-8 and 1.5-3 kpc respectively for the starburst region. By way of a series of simple assumptions, we find preliminary evidence that these hyperluminous starbursts - with star formation rates >1000 $M_\odot$ yr$^{-1}$ - are radiating at or close to their Eddington limit. Should future high resolution observations indicate that these two objects are typical of a population of high redshift Eddington-limited starbursts, this could have important consequences for models of star formation and feedback in extreme environments.

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arXiv2008

Luminous Infrared Galaxies with the Submillimeter Array: I. Survey Overview and the Central Gas to Dust Ratio

We present new data obtained with the Submillimeter Array for a sample of fourteen nearby luminous and ultraluminous infrared galaxies. The galaxies were selected to have luminosity distances D < 200 Mpc and far-infrared luminosities log(L_FIR) > 11.4. The galaxies were observed with spatial resolutions of order 1 kpc in the CO J=3-2, CO J=2-1, 13CO J=2-1, and HCO+ J=4-3 lines as well as the continuum at 880 microns and 1.3 mm. We have combined our CO and continuum data to measure an average gas-to-dust mass ratio of 120 +/- 28 (rms deviation 109) in the central regions of these galaxies, very similar to the value of 150 determined for the Milky Way. This similarity is interesting given the more intense heating from the starburst and possibly accretion activity in the luminous infrared galaxies compared to the Milky Way. We find that the peak H_2 surface density correlates with the far-infrared luminosity, which suggests that galaxies with higher gas surface densities inside the central kiloparsec have a higher star formation rate. The lack of a significant correlation between total H_2 mass and far-infrared luminosity in our sample suggests that the increased star formation rate is due to the increased availability of molecular gas as fuel for star formation in the central regions. In contrast to previous analyses by other authors, we do not find a significant correlation between central gas surface density and the star formation efficiency, as trace by the ratio of far-infrared luminosity to nuclear gas mass. Our data show that it is the star formation rate, not the star formation efficiency, that increases with increasing central gas surface density in these galaxies.

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arXiv2008

Spitzer IRAC Infrared Colours of Submillimetre-bright Galaxies

High-redshift submillimetre-bright galaxies identified by blank field surveys at millimetre and submillimetre wavelengths appear in the region of the IRAC colour-colour diagrams previously identified as the domain of luminous active galactic nuclei (AGNs). Our analysis using a set of empirical and theoretical dusty starburst spectral energy distribution (SED) models shows that power-law continuum sources associated with hot dust heated by young (<100 Myr old), extreme starbursts at z>2 also occupy the same general area as AGNs in the IRAC colour-colour plots. A detailed comparison of the IRAC colours and SEDs demonstrates that the two populations are distinct from each other, with submillimetre-bright galaxies having a systematically flatter IRAC spectrum (>1 mag bluer in the observed [4.5]-[8.0] colour). Only about 20% of the objects overlap in the colour-colour plots, and this low fraction suggests that submillimetre galaxies powered by a dust-obscured AGN are not common. The red IR colours of the submillimetre galaxies are distinct from those of the ubiquitous foreground IRAC sources, and we propose a set of IR colour selection criteria for identifying SMG counterparts that can be used even in the absence of radio or Spitzer MIPS 24 micron data.

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arXiv2008

Galaxy Evolution in Hickson Compact Groups: The Role of Ram Pressure Stripping and Strangulation

Galaxies in compact groups tend to be deficient in neutral hydrogen compared to isolated galaxies of similar optical properties. In order to investigate the role played by a hot intragroup medium (IGM) for the removal and destruction of HI in these systems, we have performed a Chandra and XMM-Newton study of eight of the most HI deficient Hickson compact groups. Diffuse X-ray emission associated with an IGM is detected in four of the groups, suggesting that galaxy-IGM interactions are not the dominant mechanism driving cold gas out of the group members. No clear evidence is seen for any of the members being currently stripped of any hot gas, nor for galaxies to show enhanced nuclear X-ray activity in the X-ray bright or most HI deficient groups. Combining the inferred IGM distributions with analytical models of representative disc galaxies orbiting within each group, we estimate the HI mass loss due to ram pressure and viscous stripping. While these processes are generally insufficient to explain observed HI deficiencies, they could still be important for HI removal in the X-ray bright groups, potentially removing more than half of the ISM in the X-ray bright HCG 97. Ram pressure may also have facilitated strangulation through the removal of galactic coronal gas. In X-ray undetected groups, tidal interactions could be playing a prominent role, but it remains an open question whether they can fully account for the observed HI deficiencies.

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