Galaxy Interactions in Compact Groups II: abundance and kinematic anomalies in HCG 91c

Galaxies in Hickson Compact Group 91 (HCG 91) were observed with the WiFeS integral field spectrograph as part of our ongoing campaign targeting the ionized gas physics and kinematics inside star forming members of compact groups. Here, we report the discovery of HII regions with abundance and kinematic offsets in the otherwise unremarkable star forming spiral HCG 91c. The optical emission line analysis of this galaxy reveals that at least three HII regions harbor an oxygen abundance ~0.15 dex lower than expected from their immediate surroundings and from the abundance gradient present in the inner regions of HCG 91c. The same star forming regions are also associated with a small kinematic offset in the form of a lag of 5-10 km/s with respect to the local circular rotation of the gas. HI observations of HCG 91 from the Very Large Array and broadband optical images from Pan-STARRS suggest that HCG 91c is caught early in its interaction with the other members of HCG 91. We discuss different scenarios to explain the origin of the peculiar star forming regions detected with WiFeS, and show that evidence point towards infalling and collapsing extra-planar gas clouds at the disk-halo interface, possibly as a consequence of long-range gravitational perturbations of HCG 91c from the other group members. As such, HCG 91c provides evidence that some of the perturbations possibly associated with the early phase of galaxy evolution in compact groups impact the star forming disk locally, and on sub-kpc scales.Comment: 25 pages, 21 figures, MNRAS accepted. Until publication of the article, the interactive component of Figure 4 is available at this URL: http://www.mso.anu.edu.au/~fvogt/website/misc.htm

Comments on SUSY inflation models on the brane

In this paper we consider a class of inflation models on the brane where the dominant part of the inflaton scalar potential does not depend on the inflaton field value during inflation. In particular, we consider supernatural inflation, its hilltop version, A-term inflation, and supersymmetric (SUSY) D- and F-term hybrid inflation on the brane. We show that the parameter space can be broadened, the inflation scale generally can be lowered, and still possible to have the spectral index $n_s=0.96$.Comment: 7 page

The Cosmological Constant and Advanced Gravitational Wave Detectors

Interferometric gravitational wave detectors could measure the frequency sweep of a binary inspiral [characterized by its chirp mass] to high accuracy. The observed chirp mass is the intrinsic chirp mass of the binary source multiplied by $(1+z)$, where $z$ is the redshift of the source. Assuming a non-zero cosmological constant, we compute the expected redshift distribution of observed events for an advanced LIGO detector. We find that the redshift distribution has a robust and sizable dependence on the cosmological constant; the data from advanced LIGO detectors could provide an independent measurement of the cosmological constant.Comment: 13 pages plus 5 figure, LaTeX. Revised and final version, to appear in Phys. Rev.

The Radio-to-Submm Spectral Index as a Redshift Indicator

We present models of the 1.4 GHz to 350 GHz spectral index, alpha(350/1.4), for starburst galaxies as a function of redshift. The models include a semi-analytic formulation, based on the well quantified radio-to-far infrared correlation for low redshift star forming galaxies, and an empirical formulation, based on the observed spectrum of the starburst galaxies M82 and Arp 220. We compare the models to the observed values of alpha(350/1.4) for starburst galaxies at low and high redshift. We find reasonable agreement between the models and the observations, and in particular, that an observed spectral index of alpha(350/1.4) > +0.5 indicates that the target source is likely to be at high redshift, z > 1. The evolution of alpha(350/1.4) with redshift is mainly due to the very steep rise in the Raleigh-Jeans portion of the thermal dust spectrum shifting into the 350 GHz band with increasing redshift. We also discuss situations where this relationship could be violated. We then apply our models to examine the putative identifications of submm sources in the Hubble Deep Field, and conclude that the submm sources reported by Hughes et al. are likely to be at high redshifts, z > 1.5.Comment: standard LATEX file plus 1 postscript figure. Added references and revised figure. second figure revision. Final Proof version. to appear in Astrophysical Journal Letter

High resolution imaging of molecular line emission from high redshift QSOs

We present moderate (1'') and high resolution (0.2'') observations of the CO(2-1) emission at 43 GHz, and radio continuum emission at 1.47 GHz, from the z=4.7 QSO BRI 1202-0725 and the z=4.4 QSO BRI 1335--0417 using the Very Large Array. The moderate resolution observations show that in both cases the CO emission is spatially resolved into two components separated by 1'' for 1335-0417 and 4'' for 1202-0725. The high resolution observations show that each component has sub-structure on scales of 0.2'' to 0.5'', with intrinsic brightness temperatures > 20K. The CO ladder from (2-1) up to (7-6) suggests a high kinetic temperature for the gas (70 K), and a high column density (10^{24} cm^{-2}). In both sources the continuum-to-line ratio: L_{FIR}/L'_{CO(1-0)} = 335. All these characteristics (brightness temperature, excitation temperature, column density, and continuum-to-line ratio) are comparable to conditions found in low redshift, ultra-luminous nuclear starburst galaxies. We find that the CO emitting regions in 1202-0725 and 1335-0417 must be close to face-on in order to avoid having the gas mass exceed the gravitational mass, implying perhaps unreasonably large rotational velocities. While this problem is mitigated by lowering the CO luminosity-to-H_2 mass conversion factor (X), the required X values become comparable to, or lower than, the minimum values dictated by optically thin CO emission. We considered the possibility of magnification by gravitational lensing in order to reduce the molecular gas masses.Comment: aastex 12 postscript figures. to appear in the Astronomical Journa

Growth of GaN films on porous SiC substrate by molecular-beam epitaxy

Porous SiC (PSiC) substrates were used for the growth of GaN by reactive molecular-beam epitaxy with ammonia as the nitrogen source. Improved quality of GaNfilms has been demonstrated for growth on PSiC substrates, as compared to that on standard 6H–SiC substrates. Cross-sectional transmission electron microscopy and electron diffraction showed a reduction in dislocation density and a higher degree of lattice and thermal relaxation in the GaNfilmsgrown on porous substrates. The submicron GaNfilms exhibit a rocking curve linewidth of 3.3 arcmin for (0002) diffraction and 13.7 arcmin for (101̄2) diffraction. Low-temperature photoluminescence showed an excitonic transition with a full width at half maximum of 9.5 meV at 15 K, as well as high quantum efficiency, on the GaN layer grown on PSiC when the thin skin layer on porous SiC was removed before growth

Strong Far-IR Cooling Lines, Peculiar CO Kinematics and Possible Star Formation Suppression in Hickson Compact Group 57

We present [C II] and [O I] observations from Herschel and CO(1-0) maps from the Combined Array for{\dag} Research in Millimeter Astronomy (CARMA) of the Hickson Compact Group HCG 57, focusing on the galaxies HCG 57a and HCG 57d. HCG 57a has been previously shown to contain enhanced quantities of warm molecular hydrogen consistent with shock and/or turbulent heating. Our observations show that HCG 57d has strong [C II] emission compared to L$_{\rm FIR}$ and weak CO(1-0), while in HCG 57a, both the [C II] and CO(1-0) are strong. HCG 57a lies at the upper end of the normal distribution of [C II]/CO and [C II]/FIR ratios, and its far-IR cooling supports a low density warm diffuse gas that falls close to the boundary of acceptable PDR models. However, the power radiated in the [C II] and warm H$_2$ emission have similar magnitudes, as seen in other shock-dominated systems and predicted by recent models. We suggest that shock-heating of the [C II] is a viable alternative to photoelectric heating in violently disturbed diffuse gas. The existence of shocks is also consistent with peculiar CO kinematics in the galaxy, indicating highly non-circular motions are present. These kinematically disturbed CO regions also show evidence of suppressed star formation, falling a factor of 10-30 below normal galaxies on the Kennicutt-Schmidt relation. We suggest that the peculiar properties of both galaxies are consistent with a highly dissipative off-center collisional encounter between HCG 57d and 57a, creating ring-like morphologies in both systems. Highly dissipative gas-on-gas collisions may be more common in dense groups because of the likelihood of repeated multiple encounters. The possibility of shock-induced SF suppression may explain why a subset of these HCG galaxies have been found previously to fall in the mid-infrared green valley.Comment: ApJ accepted, 16 pages, 12 figures, 3 table

Redshifted Neutral Hydrogen 21cm Absorption toward Red Quasars

We have searched for redshifted neutral hydrogen 21cm absorption toward sources from the Stickel et al. `red quasar' sub-sample. Five of these red quasars have been searched for redshifted HI 21cm absorption to optical depth levels of a few percent, and four show strong absorption. This 80% success rate for the red quasars compares to the much lower success rate of only 11% for detecting HI 21cm absorption associated with optically selected Mg II absorption line systems. The large neutral hydrogen column densities seen toward the red quasars provide circumstantial evidence supporting the dust reddening hypothesis, as opposed to an intrinsically red spectrum for the AGN emission mechanism. The data on the red quasar sub-sample support the models of Fall and Pei for dust obscuration by damped Ly alpha absorption line systems and suggest that: (i) there may be a significant, but not dominant, population of quasars missing from optically selected samples due to dust obscuration, perhaps as high as 20% at the POSS limit for an optical sample with a redshift distribution similar to the 1 Jy, flat spectrum quasar sample, and (ii) optically selected samples may miss about half the high column density quasar absorption line systems. The redshifted HI 21cm absorption line detections are toward the sources: 0108+388 at z = 0.6685, 0500+019 at z = 0.5846, and 1504+377 at z = 0.6733. No absorption is seen toward 2149+056 at z = 0.740 at a level below that seen for the three detections. In some systems the absorbing gas is in the vicinity of the AGN, either circumnuclear material or material in the general ISM of the AGN's host galaxy, and in other systems the absorption is by gas associated with galaxies cosmologically distributed along the line of sight to the quasar