160 research outputs found
On the Radio Polarization Signature of Efficient and Inefficient Particle Acceleration in Supernova Remnant SN 1006
We present a radio polarization study of SN 1006, based on combined VLA and
ATCA observations at 20 cm that resulted in sensitive images with an angular
resolution of 10 arcsec. The fractional polarization in the two bright radio
and X-ray lobes of the SNR is measured to be 0.17, while in the southeastern
sector, where the radio and non-thermal X-ray emission are much weaker, the
polarization fraction reaches a value of 0.6 +- 0.2, close to the theoretical
limit of 0.7. We interpret this result as evidence of a disordered, turbulent
magnetic field in the lobes, where particle acceleration is believed to be
efficient, and a highly ordered field in the southeast, where the acceleration
efficiency has been shown to be very low. Utilizing the frequency coverage of
our observations, an average rotation measure of ~12 rad/m2 is determined from
the combined data set, which is then used to obtain the intrinsic direction of
the magnetic field vectors. While the orientation of magnetic field vectors
across the SNR shell appear radial, a large fraction of the magnetic vectors
lie parallel to the Galactic Plane. Along the highly polarized southeastern
rim, the field is aligned tangent to the shock, and therefore also nearly
parallel to the Galactic Plane. These results strongly suggest that the ambient
field surrounding SN 1006 is aligned with this direction (i.e., from northeast
to southwest) and that the bright lobes are due to a polar cap geometry. Our
study establishes that the most efficient particle acceleration and generation
of magnetic turbulence in SN 1006 is attained for shocks in which the magnetic
field direction and shock normal are quasi-parallel, while inefficient
acceleration and little to no generation of magnetic turbulence obtains for the
quasi-perpendicular case.Comment: Accepted for publication in Astronomical Journa
ECO and RESOLVE: Galaxy Disk Growth in Environmental Context
We study the relationships between galaxy environments and galaxy properties
related to disk (re)growth, considering two highly complete samples that are
approximately baryonic mass limited into the high-mass dwarf galaxy regime, the
Environmental COntext (ECO) catalog (data release herein) and the B-semester
region of the REsolved Spectroscopy Of a Local VolumE (RESOLVE) survey. We
quantify galaxy environments using both group identification and smoothed
galaxy density field methods. We use by-eye and quantitative morphological
classifications plus atomic gas content measurements and estimates. We find
that blue early-type (E/S0) galaxies, gas-dominated galaxies, and UV-bright
disk host galaxies all become distinctly more common below group halo mass
~10^11.5 Msun, implying that this low group halo mass regime may be a preferred
regime for significant disk growth activity. We also find that blue early-type
and blue late-type galaxies inhabit environments of similar group halo mass at
fixed baryonic mass, consistent with a scenario in which blue early types can
regrow late-type disks. In fact, we find that the only significant difference
in the typical group halo mass inhabited by different galaxy classes is for
satellite galaxies with different colors, where at fixed baryonic mass red
early and late types have higher typical group halo masses than blue early and
late types. More generally, we argue that the traditional
morphology-environment relation (i.e., that denser environments tend to have
more early types) can be largely attributed to the morphology-galaxy mass
relation for centrals and the color-environment relation for satellites.Comment: 26 pages and 28 figures; v2 contains minor figure and text updates to
match final published version in ApJ; ECO data table release now available at
http://resolve.astro.unc.edu/pages/data.ph
On the Radio Polarization Signature of Efficient and Inefficient Particle Acceleration in Supernova Remnant SN 1006
Radio polarization observations provide essential information on the degree of order and orientation of magnetic fields, which themselves play a key role in the particle acceleration processes that take place in supernova remnants (SNRs). Here we present a radio polarization study of SN 1006, based on combined Very Large Array and Australia Telescope Compact Array observations at 20 cm that resulted in sensitive images with an angular resolution of 10 arcsec. The fractional polarization in the two bright radio and X-ray lobes of the SNR is measured to be 0.17, while in the southeastern sector, where the radio and non-thermal X-ray emission are much weaker, the polarization fraction reaches a value of 0.6 ± 0.2, close to the theoretical limit of 0.7. We interpret this result as evidence of a disordered, turbulent magnetic field in the lobes, where particle acceleration is believed to be efficient, and a highly ordered field in the southeast, where the acceleration efficiency has been shown to be very low. Utilizing the frequency coverage of our observations, an average rotation measure of ~12 rad m-2 is determined from the combined data set, which is then used to obtain the intrinsic direction of the magnetic field vectors. While the orientation of magnetic field vectors across the SNR shell appear to be radial, a large fraction of the magnetic vectors lie parallel to the Galactic plane. Along the highly polarized southeastern rim, the field is aligned tangent to the shock, and therefore also nearly parallel to the Galactic plane. These results strongly suggest that the ambient field surrounding SN 1006 is aligned with this direction (i.e., from northeast to southwest) and that the bright lobes are due to a polar cap geometry. Our study establishes that the most efficient particle acceleration and generation of magnetic turbulence in SN 1006 is attained for shocks in which the magnetic field direction and shock normal are quasi-parallel, while inefficient acceleration and little to no generation of magnetic turbulence are obtained for the quasi-perpendicular case.Fil: Reynoso, Estela Marta. Consejo Nacional de Investigaciónes CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de AstronomÃa y FÃsica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de AstronomÃa y FÃsica del Espacio; ArgentinaFil: Hughes, John P.. Rutgers University; Estados UnidosFil: Moffett, David A.. Furman University; Estados Unido
Polarimetric Properties of the Crab Pulsar between 1.4 and 8.4 GHz
New polarimetric observations of the Crab pulsar at frequencies between 1.4
and 8.4 GHz are presented. Additional pulse components discovered in earlier
observations (Moffett & Hankins 1996, astro-ph/9604163) are found to have high
levels of linear polarization, even at 8.4 GHz. No abrupt sweeps in position
angle are found within pulse components; however, the position angle and
rotational phase of the interpulse do change dramatically between 1.4 and 4.9
GHz. The multi-frequency profile morphology and polarization properties
indicate a non-standard origin of the emission. Several emission geometries are
discussed, but the one favored locates sites of emission both near the pulsar
surface and in the outer magnetosphere.Comment: 20 pages, 7 postscript figures, uses aaspp4 Latex style. To appear in
Volume 522 of The Astrophysical Journa
A Broadband Study of the Emission from the Composite Supernova Remnant MSH 11-62
MSH 11-62 (G291.1-0.9) is a composite supernova remnant for which radio and
X-ray observations have identified the remnant shell as well as its central
pulsar wind nebula. The observations suggest a relatively young system
expanding into a low density region. Here we present a study of MSH 11-62 using
observations with the Chandra, XMM-Newton, and Fermi observatories, along with
radio observations from the Australia Telescope Compact Array (ATCA). We
identify a compact X-ray source that appears to be the putative pulsar that
powers the nebula, and show that the X-ray spectrum of the nebula bears the
signature of synchrotron losses as particles diffuse into the outer nebula.
Using data from the Fermi LAT, we identify gamma-ray emission originating from
MSH 11-62. With density constraints from the new X-ray measurements of the
remnant, we model the evolution of the composite system in order to constrain
the properties of the underlying pulsar and the origin of the gamma-ray
emission.Comment: 12 Pages, 12 figures. Accepted for publication in the Astrophysical
Journa
The Origin of Faint Tidal Features Around Galaxies in the RESOLVE Survey
We study tidal features (TFs) around galaxies in the REsolved Spectroscopy of a Local VolumE (RESOLVE) survey. Our sample consists of 1048 RESOLVE galaxies that overlap with the DECam Legacy Survey, which reaches an r-band 3σ depth of ∼27.9 mag arcsec−2 for a 100 arcsec2 feature. Images were masked, smoothed, and inspected for TFs like streams, shells, or tails/arms. We find TFs in 17±2% of our galaxies, setting a lower limit on the true frequency. The frequency of TFs in the gas-poor (gas-to-stellar mass ratio < 0.1) subsample is lower than in the gas-rich subsample (13±3% vs. 19±2%). Within the gas-poor subsample, galaxies with TFs have higher stellar and halo masses, ∼3× closer distances to nearest neighbors (in the same group), and possibly fewer group members at fixed halo mass than galaxies without TFs, but similar specific star formation rates. These results suggest TFs in gas-poor galaxies are typically streams/shells from dry mergers or satellite disruption. In contrast, the presence of TFs around gas-rich galaxies does not correlate with stellar or halo mass, suggesting these TFs are often tails/arms from resonant interactions. Similar to TFs in gas-poor galaxies, TFs in gas-rich galaxies imply 1.7x closer nearest neighbors in the same group; however, TFs in gas-rich galaxies are associated with diskier morphologies, higher star formation rates, and higher gas content. In addition to interactions with known neighbors, we suggest that TFs in gas-rich galaxies may arise from accretion of cosmic gas and/or gas-rich satellites below the survey limit
Cosmic Ray Acceleration at the Forward Shock in Tycho's Supernova Remnant: Evidence from Chandra X-ray Observations
We present evidence for cosmic ray acceleration at the forward shock in
Tycho's supernova remnant (SNR) from three X-ray observables: (1) the proximity
of the contact discontinuity to the forward shock, or blast wave, (2) the
morphology of the emission from the rim of Tycho, and (3) the spectral nature
of the rim emission. We determine the locations of the blast wave (BW), contact
discontinuity (CD), and reverse shock (RS) around the rim of Tycho's supernova
remnant using a principal component analysis and other methods applied to new
Chandra data. The azimuthal-angle-averaged radius of the BW is 251". For the CD
and RS we find average radii of 241" and 183", respectively. Taking account of
projection effects, we find ratios of 1:0.93:0.70 (BW:CD:RS). We show these
values to be inconsistent with adiabatic hydrodynamical models of SNR
evolution. The CD:BW ratio can be explained if cosmic ray acceleration of ions
is occurring at the forward shock. The RS:BW ratio, as well as the strong Fe Ka
emission from the Tycho ejecta, imply that the RS is not accelerating cosmic
rays. We also extract radial profiles from ~34% of the rim of Tycho and compare
them to models of surface brightness profiles behind the BW for a purely
thermal plasma with an adiabatic shock. The observed morphology of the rim is
much more strongly peaked than predicted by the model, indicating that such
thermal emission is implausible here. Spectral analysis also implies that the
rim emission is non-thermal in nature, lending further support to the idea that
Tycho's forward shock is accelerating cosmic rays.Comment: 39 pages, 10 figures, accepted by Ap
The Caltech Millimeter Wave Interferometer
The Caltech Millimeter-Wave Interferometer has recently begun observations at a wavelength of 2.6 mm. We describe the instrument and some of the first results from it
The RESOLVE and ECO Gas in Galaxy Groups Initiative: The Group Finder and the Group HI–Halo Mass Relation
We present a four-step group-finding algorithm for the Gas in Galaxy Groups (G3) initiative, a spin-off of the z ∼ 0 REsolved Spectroscopy Of a Local VolumE (RESOLVE) and Environmental COntext (ECO) surveys. In preparation for future comparisons to intermediate redshift (e.g., the LADUMA survey), we design the group finder to adapt to incomplete, shallow, or nonuniform data. We use mock catalogs to optimize the group finder’s performance. Compared to friends-of-friends (with false-pair splitting), the G3 algorithm offers improved completeness and halo-mass recovery with minimal loss of purity. Combining it with the volume-limited H I census data for RESOLVE and ECO, we examine the H I content of galaxy groups as a function of group halo mass. Group-integrated H I mass M rises monotonically over halo masses M ∼ 10–10 M, pivoting in slope at M ∼ 10M, the gas-richness threshold scale. We present the first measurement of the scatter in this relation, which has a median of ∼0.3 dex and is asymmetric toward lower M I,grp. We discuss interesting tensions with theoretical predictions and prior measurements of the M–M relation. In an appendix, we release RESOLVE DR4 and ECO DR3, including updates to survey redshifts, photometry, and group catalogs, as well as a major expansion of the ECO H I inventory with value-added data products. © 2023. The Author(s). Published by the American Astronomical SocietyWe are grateful to the anonymous referee, whose feedback has improved the quality of this work. We also thank Adrienne Erickcek, Andrew Mann, Mugdha Polimera, Matthew Bershady, Joshua Oppor, Jeremy Darling, Hayley Roberts, and Amir Kazemi-Moridani for valuable feedback at varying stages of the project. Z.L.H., S.J.K., and E.R.C. acknowledge support for this research from National Science Foundation (NSF) grant AST-1814486. Z.L.H. and D.S.C. are also supported through a North Carolina Space Grant Graduate Research Fellowship. S.J.K. and D.S.C. acknowledge support from NSF grant AST-2007351. A.J.B. acknowledges support from NSF grant AST-1814421. K.M.H. acknowledges financial support from the State Agency for Research of the Spanish Ministry of Science, Innovation and Universities through the "Center of Excellence Severo Ocho" awarded to the Instituto de Astrofisica de Andalucia (SEV-2017-0709), via participation in SKA-SPAIN, funded by the Ministry of Science and Innovation (MCIN), and financial support from grant RTI2018-096228-B-C31 (MCIU/AEI/FEDER,UE)
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