Sesar, Branimir and Cohen, Judith G. and Levitan, David and Grillmair, Carl J. and Jurić, Mario and Kirby, Evan N. and Laher, Russ R. and Ofek, Eran O. and Surace, Jason A. and Kulkarni, Shrinivas R. and Prince, Thomas A. (2012) Two Distant Halo Velocity Groups Discovered by the Palomar Transient Factory. Astrophysical Journal, 755 (2). Art. No. 134. ISSN 0004-637X. doi:10.1088/0004-637X/755/2/134. https://resolver.caltech.edu/CaltechAUTHORS:20120618-134946055
![]()
|
PDF
- Published Version
See Usage Policy. 587kB | |
![]()
|
PDF
- Submitted Version
See Usage Policy. 458kB |
Use this Persistent URL to link to this item: https://resolver.caltech.edu/CaltechAUTHORS:20120618-134946055
Abstract
We report the discovery of two new halo velocity groups (Cancer groups A and B) traced by 8 distant RR Lyrae stars and observed by the Palomar Transient Factory (PTF) survey at R.A.~129°, Dec~20° (l~205°, b~32°). Located at 92 kpc from the Galactic center (86 kpc from the Sun), these are some of the most distant substructures in the Galactic halo known to date. Follow-up spectroscopic observations with the Palomar Observatory 5.1-m Hale telescope and W. M. Keck Observatory 10-m Keck I telescope indicate that the two groups are moving away from the Galaxy at v_(gsr) = 78.0+-5.6 km s^(-1) (Cancer group A) and v_(gsr) = 16.3+-7.1 km s^(-1) (Cancer group B). The groups have velocity dispersions of σ_(v_)gsr))=12.4+-5.0 km s^(-1) and σ _(v_(gsr))=14.9+-6.2 km s^(-1), and are spatially extended (about several kpc) making it very unlikely that they are bound systems, and are more likely to be debris of tidally disrupted dwarf galaxies or globular clusters. Both groups are metal-poor (median metallicities of [Fe/H]^A = -1.6 dex and [Fe/H]^B =-2.1 dex), and have a somewhat uncertain (due to small sample size) metallicity dispersion of ~0.4 dex, suggesting dwarf galaxies as progenitors. Two additional RR Lyrae stars with velocities consistent with those of the Cancer groups have been observed ~25 ° east, suggesting possible extension of the groups in that direction.
Item Type: | Article | ||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Related URLs: |
| ||||||||||||||||||||
ORCID: |
| ||||||||||||||||||||
Additional Information: | © 2012 The American Astronomical Society. Received 2012 March 7; accepted 2012 June 26; published 2012 August 2. J.G.C. and B.S. thank NSF grant AST-0908139 to J.G.C for partial support, as do S.R.K (to NSF grant AST-1009987), and C.J.G (for a NASA grant). Support for this work was provided by NASA through Hubble Fellowship grant 51256.01 awarded to E.N.K by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. We thank the referee for a thorough review and suggestions which led to an improved manuscript. B.S. would like to thank Ź. Ivezić, B. Willman, and K. Vivas for useful discussions. We thank I. Arcavi, A. Gal-Yam, P. Groot, A. Horesh, and D. Perley for observing at Keck and Palomar. We thank the staff at the Palomar Hale telescope for help and support with observations. We are grateful to the many people who have worked to make the Keck Telescope and its instruments a reality and to operate and maintain the Keck Observatory. The authors wish to extend special thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests. Without their generous hospitality, none of the observations presented herein would have been possible. This article is based on observations obtained with the Samuel Oschin Telescope as part of the Palomar Transient Factory project, a scientific collaboration between the California Institute of Technology, Columbia University, Las Cumbres Observatory, the Lawrence Berkeley National Laboratory, the National Energy Research Scientific Computing Center, the University of Oxford, and the Weizmann Institute of Science. | ||||||||||||||||||||
Group: | Space Radiation Laboratory, Palomar Transient Factory, Infrared Processing and Analysis Center (IPAC) | ||||||||||||||||||||
Funders: |
| ||||||||||||||||||||
Subject Keywords: | Galaxy: halo – Galaxy: kinematics and dynamics – Galaxy: structure – stars: variables: RR Lyrae | ||||||||||||||||||||
Issue or Number: | 2 | ||||||||||||||||||||
DOI: | 10.1088/0004-637X/755/2/134 | ||||||||||||||||||||
Record Number: | CaltechAUTHORS:20120618-134946055 | ||||||||||||||||||||
Persistent URL: | https://resolver.caltech.edu/CaltechAUTHORS:20120618-134946055 | ||||||||||||||||||||
Official Citation: | Two Distant Halo Velocity Groups Discovered by the Palomar Transient Factory Branimir Sesar et al. 2012 ApJ 755 134 | ||||||||||||||||||||
Usage Policy: | No commercial reproduction, distribution, display or performance rights in this work are provided. | ||||||||||||||||||||
ID Code: | 31938 | ||||||||||||||||||||
Collection: | CaltechAUTHORS | ||||||||||||||||||||
Deposited By: | Tony Diaz | ||||||||||||||||||||
Deposited On: | 02 Aug 2012 21:25 | ||||||||||||||||||||
Last Modified: | 09 Nov 2021 20:02 |
Repository Staff Only: item control page