arXiv subjects

Laura Chomiuk

Publications and source records attributed to Laura Chomiuk.

155 records · Page 9Linked to original sources

arXiv2012

The X-ray Evolution of the Symbiotic Star V407 Cygni during its 2010 Outburst

We present a summary of Swift and Suzaku X-ray observations of the 2010 nova outburst of the symbiotic star, V407 Cyg. The Suzaku spectrum obtained on day 30 indicates the presence of the supersoft component from the white dwarf surface, as well as optically thin component from the shock between the nova ejecta and the Mira wind. The Swift observations then allow us to track the evolution of both components from day 4 to day 150. Most notable is the sudden brightening of the optically thin component around day 20. We identify this as the time when the blast wave reached the immediate vicinity of the photosphere of the Mira. We have developed a simple model of the blast wave-wind interaction that can reproduce the gross features of the X-ray evolution of V407 Cyg, and explore a parameter space of ejected mass, binary separation and Mira mass loss rate. If the model is correct, the binary separation is likely to be larger then previously suggested and the mass loss rate of the Mira is likely to be relatively low.

astro-ph.SR↗

arXiv2011

Toward a Unification of Star Formation Rate Determinations in the Milky Way and Other Galaxies

The star formation rate (SFR) of the Milky Way remains poorly known, with often-quoted values ranging from 1 to 10 solar masses per year. This situation persists despite the potential for the Milky Way to serve as the ultimate SFR calibrator for external galaxies. We show that various estimates for the Galactic SFR are consistent with one another once they have been normalized to the same initial mass function (IMF) and massive star models, converging to 1.9 +/- 0.4 M_sun/yr. However, standard SFR diagnostics are vulnerable to systematics founded in the use of indirect observational tracers sensitive only to high-mass stars. We find that absolute SFRs measured using resolved low/intermediate-mass stellar populations in Galactic H II regions are systematically higher by factors of ~2-3 as compared with calibrations for SFRs measured from mid-IR and radio emission. We discuss some potential explanations for this discrepancy and conclude that it could be allayed if (1) the power-law slope of the IMF for intermediate-mass (1.5 M_sun < m < 5 M_sun) stars were steeper than the Salpeter slope, or (2) a correction factor was applied to the extragalactic 24 micron SFR calibrations to account for the duration of star formation in individual mid-IR-bright H II regions relative to the lifetimes of O stars. Finally, we present some approaches for testing if a Galactic SFR of ~2 M_sun/yr is consistent with what we would measure if we could view the Milky Way as external observers. Using luminous radio supernova remnants and X-ray point sources, we find that the Milky Way deviates from expectations at the 1-3 sigma level, hinting that perhaps the Galactic SFR is overestimated or extragalactic SFRs need to be revised upwards.

astro-ph.GA↗

arXiv2011

EVLA Nova Project Observations of the Classical Nova V1723 Aquilae

We present radio light curves and spectra of the classical nova V1723 Aql obtained with the Expanded Very Large Array (EVLA). This is the first paper to showcase results from the EVLA Nova Project, which comprises a team of observers and theorists utilizing the greatly enhanced sensitivity and frequency coverage of EVLA radio observations, along with observations at other wavelengths, to reach a deeper understanding of the energetics, morphology, and temporal characteristics of nova explosions. Our observations of V1723 Aql span 1-37 GHz in frequency, and we report on data from 14-175 days following the time of the nova explosion. The broad frequency coverage and frequent monitoring show that the radio behavior of V1723 Aql does not follow the classic Hubble-flow model of homologous spherically expanding thermal ejecta. The spectra are always at least partially optically thin, and the flux rises on faster timescales than can be reproduced with linear expansion. Therefore, any description of the underlying physical processes must go beyond this simple picture. The unusual spectral properties and light curve evolution might be explained by multiple emitting regions or shocked material. Indeed, X-ray observations from Swift reveal that shocks are likely present.

astro-ph.HE↗

arXiv2011

Microwave Observations of Edge-on Protoplanetary Disks: Program Overview and First Results

We are undertaking a multi-frequency Expanded Very Large Array (EVLA) survey of edge-on protoplanetary disks to probe the growth of solids in each disk, sedimentation of such material into the disk midplane, and the connection of these phenomena to the planet formation process. The projection of edge-on disk systems along our line of sight enables a study of the vertical stratification of large grains with fewer model dependencies than would be required for disks that are more face-on. Robust studies of the spatial distribution of grains up to ~1 cm in size are possible with the wavelength range and sensitivity of the EVLA. In this contribution we describe target selection and observational strategies. First results concerning the Class 0 source IRAS04368+2557 (L1527 IRS) are presented, including a study of this source's 8.46 GHz continuum variability over short and long time baselines and an indication that its protoplanetary disk may have a dearth of pebble-sized grains.

astro-ph.SR↗

arXiv2011

Unveiling Extragalactic Star Formation Using Radio Recombination Lines: An EVLA Pilot Study with NGC 253

Radio recombination lines (RRLs) are powerful, extinction-free diagnostics of the ionized gas in young, star-forming regions. Unfortunately, these lines are difficult to detect in external galaxies. We present the results of EVLA observations of the RRL and radio continuum emission at 33 GHz from NGC 253, a nearby nuclear starburst galaxy. We detect the previously unobserved H58a and H59a RRLs and make simultaneous sensitive measurements of the continuum. We measure integrated line fluxes of $44.3 \pm 0.7$ W m$^{-2}$ and $39.9 \pm 0.8$ W m$^{-2}$ for the H58a and H59a lines, respectively. The thermal gas in NGC 253 is kinematically complex with multiple velocity components. We constrain the density of the thermal gas to $1.4 - 4 \times 10^4$ cm$^{-3}$ and estimate an ionizing photon flux of $1 \times 10^{53}$ s$^{-1}$. We use the RRL kinematics and the derived ionizing photon flux to show that the nuclear region of NGC 253 is not gravitationally bound, which is consistent with the outflow of gas inferred from the X-ray and Halpha measurements. The line profiles, fluxes, and kinematics of the H58a and H59a lines agree with those of RRLs at different frequencies confirming the accuracy of the previous, more difficult, high frequency observations. We find that the EVLA is an order of magnitude more efficient for extragalactic RRL observations than the VLA. These observations demonstrate both the power of the EVLA and the future potential of extragalactic RRL studies with the EVLA.

astro-ph.GA↗

arXiv2011

The Fossil Record of Two-phase Galaxy Assembly: Kinematics and Metallicities in the Nearest S0 Galaxy

We present a global analysis of kinematics and metallicity in the nearest S0 galaxy, NGC 3115, along with implications for its assembly history. The data include high-quality wide-field imaging from Suprime-Cam on the Subaru telescope, and multi-slit spectra of the field stars and globular clusters (GCs) obtained using Keck-DEIMOS/LRIS and Magellan-IMACS. Within two effective radii, the bulge (as traced by the stars and metal-rich GCs) is flattened and rotates rapidly (v/sigma > 1.5). At larger radii, the rotation declines dramatically to v/sigma ~ 0.7, but remains well-aligned with the inner regions. The radial decrease in characteristic metallicity of both the metal-rich and metal-poor GC subpopulations produces strong gradients with power law slopes of -0.17 +/- 0.04 and -0.38 +/- 0.06 dex per dex, respectively. We argue that this pattern is not naturally explained by a binary major merger, but instead by a two-phase assembly process where the inner regions have formed in an early violent, dissipative phase, followed by the protracted growth of the outer parts via minor mergers with typical mass ratios of ~ 15-20:1.

astro-ph.CO↗

arXiv2009

A Universal Luminosity Function for Radio Supernova Remnants

We compile radio supernova remnant (SNR) samples from the literature for 19 nearby galaxies ranging from the SMC to Arp 220, and use this data to constrain the SNR luminosity function (LF) at 20 cm. We find that radio SNR populations are strikingly similar across galaxies. The LF can be described as a power law with constant index and scaling proportional to a galaxy's star formation rate (SFR). Unlike previous authors, we do not find any dependence of SNR luminosity on a galaxy's global ISM density. The observed correlation between the luminosity of a galaxy's brightest SNR and a galaxy's SFR can be completely explained by statistical effects, wherein galaxies with higher SFR more thoroughly sample the high-luminosity end of the SNR LF. The LF is well fit by a model of SNR synchrotron emission which includes diffusive shock acceleration and magnetic field amplification, if we assume that all remnants are undergoing adiabatic expansion, the densities of star-forming regions are similar across galaxies, and the efficiency of CR production is constant.

astro-ph.CO↗

arXiv2009

A Search for Radio Supernova Remnants in Four Irregular Galaxies

We survey four nearby irregular galaxies for radio supernova remnants (SNRs) using deep (1 sigma ~ 20 microJy), high resolution (~20 pc) VLA continuum data at 20, 6, and 3.6 cm. We identify discrete sources in these galaxies and use radio spectral indices and H alpha images to categorize them as SNRs, H II regions, or background radio galaxies. Our classifications are generally in good agreement agreement with the literature. We identify a total of 43 SNR candidates: 23 in NGC 1569, 7 in NGC 4214, 5 in NGC 2366, and 8 in NGC 4449. Only one SNR--the well-studied object J1228+441 in NGC 4449--is more luminous at 20 cm than Cas A. By comparing the total thermal flux density in each galaxy to that localized in H II regions, we conclude that a significant fraction must be in a diffuse component or in low-luminosity H II regions.

astro-ph.CO↗

arXiv2008

The Peculiar Globular Cluster System of the S0 Galaxy NGC 7457

We present HST photometry and Keck spectroscopy of globular clusters (GCs) in the nearby S0 galaxy NGC 7457. The V-I color-magnitude diagram of GCs lacks the clear bimodality present in most early-type galaxies; there may be a significant population of intermediate-color objects. Of 13 spectroscopically-observed GCs, two are unusually metal-rich and feature bright [O III] emission lines. We conclude that one probably hosts a planetary nebula and the other a supernova remnant. Such emission line objects should be more common in an intermediate-age stellar population than in an old one. We therefore suggest that, in addition to the typical old metal-rich and old metal-poor GC subpopulations, there may be a third subpopulation of intermediate age. Such a subpopulation may have been formed ~2-3 Gyr ago, in the same star-forming event that dominates the stellar population of the center of the galaxy.

astro-ph↗

arXiv2005

The KPNO International Spectroscopic Survey. V. H-alpha-selected Survey List 3

The KPNO International Spectroscopic Survey (KISS) is an objective-prism survey designed to detect extragalactic emission-line objects. It combines many of the features of previous slitless spectroscopic surveys with the advantages of modern CCD detectors, and is the first purely digital objective-prism survey for emission-line galaxies (ELGs). Here we present the third list of ELG candidates selected from our red spectral data, which cover the wavelength range 6400 to 7200 A. In most cases, the detected emission line is H-alpha. The current survey list covers the region of the NOAO Deep Wide-Field Survey (NDWFS). This survey covers two fields; the first is 3 x 3 degrees square and located at RA = 14h 30m, DEC = 34.5 deg (B1950), the second is 2.3 x 4.0 degrees and centered at RA = 2h 7.5m, DEC = -4.75 deg. A total area of 19.65 deg^2 is covered by the KISS data. A total of 261 candidate emission-line objects have been selected for inclusion in the survey list (13.3 per deg^2). We tabulate accurate coordinates and photometry for each source, as well as estimates of the redshift, emission-line flux and line equivalent width based on measurements of the digital objective-prism spectra. The properties of the KISS ELGs are examined using the available observational data. When combined with the wealth of multi-wavelength data already available for the NDWFS fields, the current list of KISS ELGs should provide a valuable tool for studying star-formation and nuclear activity in galaxies in the local universe.

astro-ph↗

arXiv2004

Absence of Dwarf Galaxies at High Redshifts: Evidence from a Galaxy Group

The galaxy group NGC 5044 consists of a luminous giant elliptical galaxy surrounded by a cluster of approximately 160 low luminosity and dwarf galaxies, mostly of early type. The cumulative projected radial distribution of dwarf galaxies in the NGC 5044 group, unlike distributions of more luminous galaxies in rich clusters, does not follow a projected dark matter (NFW) profile. Instead, a deficiency or absence of low luminosity galaxies is apparent in NGC 5044 within about 350 kpc, about one third of the current group virial radius. Most of the dwarf galaxies identified in NGC 5044 entered the virial radius at redshifts less than about 2 or 3, and very few entered at higher redshifts. The peculiar, non-NFW shape of the projected cumulative dwarf galaxy distribution in NGC 5044 within 350 kpc resembles the characteristic shallow cumulative distribution of dark subhalos that are also known to be relatively young. Dynamical friction is unlikely to explain the apparent lack of group member galaxies at small radii in NGC 5044.

astro-ph↗