arXiv subjects

E. J. Barton

Publications and source records attributed to E. J. Barton.

8 recordsLinked to original sources

arXiv2016

Detection of an atmosphere around the super-Earth 55 Cancri e

We report the analysis of two new spectroscopic observations of the super-Earth 55 Cancri e, in the near infrared, obtained with the WFC3 camera onboard the HST. 55 Cancri e orbits so close to its parent star, that temperatures much higher than 2000 K are expected on its surface. Given the brightness of 55 Cancri, the observations were obtained in scanning mode, adopting a very long scanning length and a very high scanning speed. We use our specialized pipeline to take into account systematics introduced by these observational parameters when coupled with the geometrical distortions of the instrument. We measure the transit depth per wavelength channel with an average relative uncertainty of 22 ppm per visit and find modulations that depart from a straight line model with a 6$σ$ confidence level. These results suggest that 55 Cancri e is surrounded by an atmosphere, which is probably hydrogen-rich. Our fully Bayesian spectral retrieval code, T-REx, has identified HCN to be the most likely molecular candidate able to explain the features at 1.42 and 1.54 $μ$m. While additional spectroscopic observations in a broader wavelength range in the infrared will be needed to confirm the HCN detection, we discuss here the implications of such result. Our chemical model, developed with combustion specialists, indicates that relatively high mixing ratios of HCN may be caused by a high C/O ratio. This result suggests this super-Earth is a carbon-rich environment even more exotic than previously thought.

astro-ph.EP↗

arXiv2011

Halo Gas and Galaxy Disk Kinematics of a Volume-Limited Sample of MgII Absorption-Selected Galaxies at z~0.1

We have directly compared MgII halo gas kinematics to the rotation velocities derived from emission/absorption lines of the associated host galaxies. Our 0.096<z<0.148 volume-limited sample comprises 13 ~L* galaxies, with impact parameters of 12-90 kpc from background quasars sight-lines, associated with 11 MgII absorption systems with MgII equivalent widths 0.3< W_r(2796)<2.3A. For only 5/13 galaxies, the absorption resides to one side of the galaxy systemic velocity and trends to align with one side of the galaxy rotation curve. The remainder have absorption that spans both sides of the galaxy systemic velocity. These results differ from those at z~0.5, where 74% of the galaxies have absorption residing to one side of the galaxy systemic velocity. For all the z~0.1 systems, simple extended disk-like rotation models fail to reproduce the full MgII velocity spread, implying other dynamical processes contribute to the MgII kinematics. In fact 55% of the galaxies are "counter-rotating" with respect to the bulk of the MgII absorption. These MgII host-galaxies are isolated, have low star formation rates (SFRs) in their central regions (<1 Msun/yr), and SFRs per unit area well below those measured for galaxies with strong winds. The galaxy NaID (stellar+ISM) and MgIb (stellar) absorption line ratios are consistent with a predominately stellar origin, implying kinematically quiescent interstellar media. These facts suggest that the kinematics of the MgII absorption halos for our sample of galaxies are not influenced by galaxy--galaxy environmental effects, nor by winds intrinsic to the host galaxies. For these low redshift galaxies, we favor a scenario in which infalling gas accretion provides a gas reservoir for low-to-moderate star formation rates and disk/halo processes.

astro-ph.CO↗

arXiv2010

Herschel-ATLAS: blazars in the SDP field

To investigate the poorly constrained sub-mm counts and spectral properties of blazars we searched for these in the Herschel-ATLAS (H-ATLAS) science demostration phase (SDP) survey catalog. We cross-matched 500$μ$m sources brighter than 50 mJy with the FIRST radio catalogue. We found two blazars, both previously known. Our study is among the first blind blazar searches at sub-mm wavelengths, i.e., in the spectral regime where little is still known about the blazar SEDs, but where the synchrotron peak of the most luminous blazars is expected to occur. Our early results are consistent with educated extrapolations of lower frequency counts and question indications of substantial spectral curvature downwards and of spectral upturns at mm wavelengths. One of the two blazars is identified with a Fermi/LAT $γ$-ray source and a WMAP source. The physical parameters of the two blazars are briefly discussed.These observations demonstrate that the H-ATLAS survey will provide key information about the physics of blazars and their contribution to sub-mm counts.

astro-ph.CO↗

arXiv2009

Type IIn supernovae at z ~ 2 from archival data

Supernovae have been confirmed to redshift z ~ 1.7 for type Ia (thermonuclear detonation of a white dwarf) and to z ~ 0.7 for type II (collapse of the core of the star). The subclass type IIn supernovae are luminous core-collapse explosions of massive stars and, unlike other types, are very bright in the ultraviolet, which should enable them to be found optically at redshifts z ~ 2 and higher. In addition, the interaction of the ejecta with circumstellar material creates strong, long-lived emission lines that allow spectroscopic confirmation of many events of this type at z ~ 2 for 3 - 5 years after explosion. Here we report three spectroscopically confirmed type IIn supernovae, at redshifts z = 0.808, 2.013 and 2.357, detected in archival data using a method designed to exploit these properties at z ~ 2. Type IIn supernovae directly probe the formation of massive stars at high redshift. The number found to date is consistent with the expectations of a locally measured stellar initial mass function, but not with an evolving initial mass function proposed to explain independent observations at low and high redshift.

astro-ph.CO↗

arXiv2005

First Light and Reionization: A Conference Summary

The search for the first illuminated astronomical sources in the universe is at the edge of the cosmic frontier. Promising techniques for discovering the first objects and their effects span the electromagnetic spectrum and include gravitational waves. We summarize a workshop on discovering and understanding these sources which was held in May 2005 through the Center for Cosmology at the University of California, Irvine.

astro-ph↗

arXiv2005

Metallicity and Nuclear Star Formation in Nearby Galaxy Pairs: Evidence for Tidally Induced Gas Flows

We derive the first luminosity-metallicity relation for a large objectively selected sample of local galaxy pairs and we compare the pairs LZ relation with the relation for the Nearby Field Galaxy Survey (NFGS). Galaxy pair members with small projected separations (s<20 kpc/h) have systematically lower metallicities (~0.2 dex on average) than the field galaxies, or than more widely separated pairs at the same luminosity. There is a strong correlation between metallicity and central burst strength in the galaxy pairs. All five galaxies in the pairs sample with strong central bursts have close companions and metallicities lower than the comparable field galaxies. Our results provide strong observational evidence for a merger scenario where galaxy interactions cause gas flows towards the central regions, carrying less enriched gas from the outskirts of the galaxy into the central regions. The less enriched gas dilutes the pre-existing nuclear gas to produce a lower metallicity than would be obtained prior to the interaction. These gas flows trigger central bursts of star formation, causing strong central burst strengths, and possibly aiding the formation of blue bulges. We show that the timescale and central gas dilution required by this scenario are consistent with predictions from hydrodynamic merger models.

astro-ph↗

arXiv2004

Stellar Populations of Dwarf Elliptical Galaxies: UBVRI Photometry of Dwarf Elliptical Galaxies in the Virgo Cluster

We present UBVRI surface photometry for 16 dwarf elliptical galaxies in the Virgo Cluster with previously measured kinematic properties. The global optical colors are red, with median values for the sample of 0.24 +/- 0.03 in (U-B), 0.77 +/- 0.02 in (B-V), and 1.02 +/- 0.03 in (V-I). We recover the well known color-magnitude relation for cluster galaxies, but find no significant difference in dominant stellar population between rotating and non-rotating dwarf elliptical galaxies; the average age of the dominant stellar population is 5-7 Gyr in all 16 galaxies in this sample. Analysis of optical spectra confirm these age estimates and indicate Fe and Mg abundances in the range of 1/20th to 1/3 of solar, as expected for low luminosity galaxies. Based on Lick indices and simple stellar population models, the derived [alpha/Fe] ratios are sub-solar to solar, indicating a more gradual chemical enrichment history for dEs as compared to giant elliptical galaxies in the Virgo Cluster. These observations confirm the marked difference in stellar population and stellar distribution between dwarf and giant elliptical galaxies and further substantiate the need for alternative evolutionary scenarios for the lowest mass cluster galaxies. We argue that it is likely that several different physical mechanisms played a significant role in the production of the Virgo cluster dE galaxies including in situ formation, infall of dEs that were once part of Local Group analogs, and transformation of dwarf irregular galaxies by the cluster environment. The observations support the hypothesis that a large fraction of the Virgo cluster dEs are formed by ram pressure stripping of gas from infalling dIs.

astro-ph↗

arXiv1998

Environments of Redshift Survey Compact Groups of Galaxies

Redshift Survey Compact Groups (RSCGs) are tight knots of N >= 3 galaxies selected from the CfA2+SSRS2 redshift survey. The selection is based on physical extent and association in redshift space alone. We measured 300 new redshifts of fainter galaxies within 1 h^{-1} Mpc of 14 RSCGs to explore the relationship between RSCGs and their environments. 13 of 14 RSCGs are embedded in overdense regions of redshift space. The systems range from a loose group of 5 members to an Abell cluster. The remaining group, RSCG 64, appears isolated. RSCGs are isolated and distinct from their surroundings to varying degrees, as are the Hickson Compact Groups. Among the 13 embedded RSCGs, 3 are distinct from their general environments (RSCG 9, RSCG 11 and RSCG 85).

astro-ph↗