James Lloyd Higdon

Hubble Space Telescope Morphologies of z ~ 2 Dust Obscured Galaxies. I. Power-Law Sources

We present high-spatial resolution optical and near-infrared imaging obtained using the ACS, WFPC2, and NICMOS cameras aboard the Hubble Space Telescope of 31 24 μm bright z ≈ 2 Dust Obscured Galaxies (DOGs) identified in the Bootes Field of the NOAO Deep Wide-Field Survey. Although this subset of DOGs have mid-IR spectral energy distributions dominated by a power-law component suggestive of an AGN, all but one of the galaxies are spatially extended and not dominated by an unresolved component at rest-frame UV or optical wavelengths. The observed V – H and I-H colors of the extended components are 0.2-3 magnitudes redder than normal star-forming galaxies. All but one have axial ratios >0.3, making it unlikely that DOGs are composed of an edge-on star-forming disk. We model the spatially extended component of the surface brightness distributions of the DOGs with a Sersic profile and find effective radii of 1-6 kpc. This sample of DOGs is smaller than most submillimeter galaxies (SMGs), but larger than quiescent high-redshift galaxies. Nonparametric measures (Gini and M_20) of DOG morphologies suggest that these galaxies are more dynamically relaxed than local ULIRGs. We estimate lower limits to the stellar masses of DOGs based on the rest-frame optical photometry and find that these range from ~10^9-10^(11) M☉ . If major mergers are the progenitors of DOGs, then these observations suggest that DOGs may represent a postmerger evolutionary stage.

A 500 kpc H I EXTENSION OF THE VIRGO PAIR NGC 4532/DDO 137 DETECTED BY THE ARECIBO LEGACY FAST ALFA (ALFALFA) SURVEY

We report the discovery of a ~500 kpc H I extension southwest of the Virgo Cluster H I-rich pair NGC 4532/DDO 137, detected as part of the Arecibo Legacy Fast ALFA (ALFALFA) Survey. The feature is the longest and most massive H I tail structure so far found in the Virgo Cluster and, at 1.8 Mpc from M87, the most distant from the main concentration of the intracluster medium. The structure is spatially and spectrally separated into two ridges and is defined by diffuse emission and discrete clumps of mass (2.5–6.8) × 107 M☉. All emission is blueshifted with respect to the NGC 4532/DDO 137 pair emission. Including diffuse emission, the structure has a total mass of up to 7 × 108 M☉, equivalent to ~10% of the systems H I mass. Optical R-band imaging finds no counterparts to a level of 26.5 mag arcsec−2. The characteristics of the structure appear most consistent with a tidal origin.

The Second-generation z (Redshift) and Early Universe Spectrometer. I. First-light Observation of a Highly Lensed Local-ulirg Analog at High-z

We recently commissioned our new spectrometer, the second-generation z(Redshift) and Early Universe Spectrometer (ZEUS-2) on the Atacama Pathfinder Experiment telescope. ZEUS-2 is a submillimeter grating spectrometer optimized for detecting the faint and broad lines from distant galaxies that are redshifted into the telluric windows from 200 to 850 μm. It uses a focal plane array of transition-edge sensed bolometers, the first use of these arrays for astrophysical spectroscopy. ZEUS-2 promises to be an important tool for studying galaxies in the years to come because of its synergy with Atacama Large Millimeter Array and its capabilities in the short submillimeter windows that are unique in the post-Herschel era. Here, we report on our first detection of the [C II] 158 μm line with ZEUS-2. We detect the line at z ~ 1.8 from H-ATLAS J091043.1–000322 with a line flux of (6.44 ± 0.42) × 10^(–18) W m^(–2). Combined with its far-IR luminosity and a new Herschel-PACS detection of the [O I] 63 μm line, we model the line emission as coming from a photo-dissociation region with far-ultraviolet radiation field, G ~ 2 × 10^4 G_0, gas density, n ~ 1 × 10^3 cm^(–3) and size between ~0.4 and 1 kpc. On the basis of this model, we conclude that H-ATLAS J091043.1–000322 is a high-redshift analog of a local ultra-luminous IR galaxy; i.e., it is likely the site of a compact starburst caused by a major merger. Further identification of these merging systems is important for constraining galaxy formation and evolution models.

Spitzer 70/160 μm observations of high-redshift ULIRGs and HyLIRGs in the Boötes field

We present new 70 and 160 μm observations of a sample of extremely red (R – [24] ≳ 15 mag), mid-infrared bright, high-redshift (1.7 ≾ z ≾ 2.8) galaxies. All targets detected in the far-infrared exhibit rising spectral energy distributions (SEDs) consistent with dust emission from obscured active galactic nuclei (AGNs) and/or star-forming regions in luminous IR galaxies (LIRGs). We find that the SEDs of the high-redshift sources are more similar to canonical AGN-dominated local ultraluminous IR galaxies (ULIRGs) with significant warm dust components than to typical local star-forming ULIRGs. The inferred IR (8-1000 μm) bolometric luminosities are found to be Lbol ~ 4 × 10^12 L⊙ to ~3 × 10^13 L⊙ (ULIRGs/hyper-luminous IR galaxies (HyLIRGs)), representing the first robust constraints on Lbol for this class of object.

Radio and Infrared Selected Optically Invisible Sources in the Boötes NDWFS

We have combined data from the NOAO Deep Wide-Field Survey in Bo?tes and the Spitzer Space Telescope to determine basic properties for 16 optically invisible MIPS 24 ?m and 35 optically invisible radio sources (OIMSs and OIRSs, respectively), including their spectral energy distributions (SEDs) and luminosities. Most OIMSs possess steep power-law SEDs over -->?rest = 1?10 ? m , indicating the presence of obscured AGNs in agreement with Spitzer spectroscopy. These objects are extremely luminous at rest-frame near- and mid-IR -->[? L?(5 ? m) ? 1038?1039 W], consistent with accretion near the Eddington limit and further implying that they host buried QSOs. The majority of the IRAC-detected OIRSs have flat 3.6-24 ?m SEDs, implying comparable emission from stellar photospheres and hot AGN-illuminated dust. This may reflect relatively small amounts of dust close to the central engine or current low mass accretion rates. A small subset of OIRSs appear to be starburst-dominated with photometric redshifts from 1.0 to 4.5. The OIMSs and OIRSs with significant starburst components have similar -->LK and stellar masses ( -->M* ? 1011 M -->?) assuming minimal AGN contribution. Roughly half of the OIRSs are not detected by Spitzer IRAC or MIPS. These are most likely -->z 2 radio galaxies. The IRAC-detected OIRSs are more likely than OIMSs to appear nonpointlike in the 3.6 and 4.5 ?m images, suggesting that interactions play a role in triggering their activity. The AGN-powered OIMSs may represent submillimeter galaxies making the transition from starburst to accretion dominance in their evolution to current-epoch massive ellipticals.

VLT observations of NGC 1097's "dog-leg" tidal stream Dwarf spheroidals and tidal streams

Aims. We investigate the structure and stellar population of two large stellar condensations (knots A & B) along one of the faint optical “jet-like” tidal streams associated with the spiral NGC 1097, with the goal of establishing their physical association with the galaxy and their origin. Methods. We use the VLT/FORS2 to get deep V-band imaging and low-resolution optical spectra of two knots along NGC 1097’s northeast “dog-leg” tidal stream. With this data, we explore their morphology and stellar populations. Results. Spectra were obtained for eleven sources in the field surrounding the tidal stream. The great majority of them turned out to be background or foreground sources, but the redshift of knot A (and perhaps of knot B) is consistent with that of NGC 1097. Using the V-band image of the “dog-leg” tidal feature we find that the two knots match the photometric scaling relations of canonical dwarf spheroidal galaxies (dSph) very well. Spectral analysis shows that knot A is mainly composed of stars near G-type, with no signs of ongoing star formation. Comparing its spectrum with a library of high resolution spectra of galactic globular clusters (GCs), we find that the stellar population of this dSph-like object is most similar to intermediate to metal rich galactic GCs. We find moreover, that the tidal stream shows an “S” shaped inflection as well as a pronounced stellar overdensity at knot A’s position. This suggests that knot A is being tidally stripped, and populating the stellar stream with its stars. Conclusions. We have discovered that two knots along NGC 1097’s northeast tidal stream share most of their spectral and photometric properties with ordinary dwarf spheroidal galaxies (dSph). Moreover, we find strong indications that the “dog-leg” tidal stream arises from the tidal disruption of knot A. Since it has been demonstrated that tidally stripping dSph galaxies need to loose most of their dark matter before starting to loose stars, we suggest that knot A is at present a CDM-poor object.

Radio continuum imaging of the R Coronae Austrinae star-forming region with the ATCA

Aims. The aim of this study is to investigate the nature of radio sources associated with young stellar objects (YSOs) belonging to the R CrA cluster. By combining the centimetre radio data with the wealth of shorter wavelength data accumulated recently we wish to refine estimates of the evolutionary stages of the YSOs. Methods. The region was imaged at 3, 6, and 20 cm using the Australia Telescope Compact Array. Fluxes and spectral indices for the brightest radio sources were derived from these observations. Some of the 3 and 6 cm data were obtained simultaneously, which is useful for reliable spectral index determinations of variable sources. Results. Eight pointlike sources were detected. Seven of them can be assigned to YSOs, which have counterparts in the X-rays, infrared or submm. One of the YSOs, Radio Source 9, is a Class 0 candidate, and another, IRS 7B, is suggested to be in the Class 0/I transition stage. IRS 7B is associated with extended radio lobes at 6 and 20 cm. The lobes may have a gyrosynchrotron emission component, which could be understood in terms of Fermi accleration in shocks. The Class I objects detected here seem to be a mixed lot. One of these, the wide binary IRS 5, shows a negative spectral index, rapid variability, and a high degree of circular polarisation with V/I ≈ 33% on one of the days of observation. These signs of magnetic activity suggest that at least one of the binary components has advanced beyond the Class I stage. The radio source without YSO assigment, Radio Source 5, has been suggested to be a brown dwarf. The radio properties, in particular its persistent strong emission, do not support this classification. Conclusions. The radio characteristics of the detected YSOs roughly agree with the scheme where the dominant emission mechanism changes with age. The heterogeneity of the Class I group can possibly be explained by a drastic decline in the jet activity during this stage, which also changes the efficiency of free-free absorption around the protostar.

MOLECULAR GAS AND STAR FORMATION IN THE CARTWHEEL

Atacama Large Millimeter/submillimeter Array (ALMA) 12CO(J=1-0) observations are used to study the cold molecular ISM of the Cartwheel ring galaxy and its relation to HI and massive star formation (SF). CO moment maps find

STAR FORMATION AND THE INTERSTELLAR MEDIUM IN NEARBY TIDAL STREAMS (SAINTS): SPITZER MID-INFRARED SPECTROSCOPY AND IMAGING OF INTERGALACTIC STAR-FORMING OBJECTS

(2.69\pm0.05)\times10^{9}

Detection of [O iii] at z ∼ 3: A Galaxy Above the Main Sequence, Rapidly Assembling Its Stellar Mass

M