Variable Stars in the Giant Satellite Galaxy Antlia 2

We report 350 pulsating variable stars found in four DECam fields (∼12 deg2) covering the Antlia 2 satellite galaxy. The sample of variables includes 318 RR Lyrae stars and eight anomalous Cepheids in the galaxy. Reclassification of several objects designated previously to be RR Lyrae as anomalous Cepheids get rid of the satellite’s stars intervening along the line of sight. This in turn removes the need for prolific tidal disruption of the dwarf, in agreement with the recently updated proper motion and pericenter measurements based on Gaia EDR3. There are also several bright foreground RR Lyrae stars in the field, and two distant background variables located ∼45 kpc behind Antlia 2. We found RR Lyrae stars over the full search area, suggesting that the galaxy is very large and likely extends beyond our observed area. The mean period of the RRab in Antlia 2 is 0.599 days, while the RRc have a mean period of 0.368 days, indicating the galaxy is an Oosterhoff-intermediate system. The distance to Antlia 2 based on the RR Lyrae stars is 124.1 kpc (μ 0 = 20.47) with a dispersion of 5.4 kpc. We measured a clear distance gradient along the semimajor axis of the galaxy, with the southeast side of Antlia 2 being ∼13 kpc farther away from the northwest side. This elongation along the line of sight is likely due to the ongoing tidal disruption of Ant 2.

[1]  Sergey E. Koposov,et al.  Measuring the Mass of the Large Magellanic Cloud with Stellar Streams Observed by S 5 , 2021, The Astrophysical Journal.

[2]  Sergey E. Koposov,et al.  Kinematics of Antlia 2 and Crater 2 from the Southern Stellar Stream Spectroscopic Survey (S 5) , 2021, The Astrophysical Journal.

[3]  P. J. Richards,et al.  Gaia Early Data Release 3: Summary of the contents and survey properties , 2020, 2012.01533.

[4]  A. Koch,et al.  The age of the Milky Way inner stellar spheroid from RR Lyrae population synthesis , 2020, Astronomy & Astrophysics.

[5]  Sergey E. Koposov,et al.  Broken into Pieces: ATLAS and Aliqa Uma as One Single Stream , 2020, The Astrophysical Journal.

[6]  J. Frieman,et al.  Milky Way Satellite Census. I. The Observational Selection Function for Milky Way Satellites in DES Y3 and Pan-STARRS DR1 , 2019, The Astrophysical Journal.

[7]  D. Nidever,et al.  A DECam view of the diffuse dwarf galaxy Crater II – Variable stars , 2019, Monthly Notices of the Royal Astronomical Society.

[8]  M. Nonino,et al.  On the Use of Field RR Lyrae as Galactic Probes. I. The Oosterhoff Dichotomy Based on Fundamental Variables , 2019, The Astrophysical Journal.

[9]  J. Simon,et al.  The Faintest Dwarf Galaxies , 2019, Annual Review of Astronomy and Astrophysics.

[10]  Sergey E. Koposov,et al.  The total mass of the Large Magellanic Cloud from its perturbation on the Orphan stream , 2018, Monthly Notices of the Royal Astronomical Society.

[11]  A. Walker,et al.  The Population of Pulsating Variable Stars in the Sextans Dwarf Spheroidal Galaxy , 2018, The Astronomical Journal.

[12]  Sergey E. Koposov,et al.  The hidden giant: discovery of an enormous Galactic dwarf satellite in Gaia DR2 , 2018, Monthly Notices of the Royal Astronomical Society.

[13]  Gregory M. Green.  dustmaps: A Python interface for maps of interstellar dust , 2018, Journal of Open Source Software.

[14]  et al,et al.  Gaia Data Release 2 , 2018, Astronomy & Astrophysics.

[15]  F. Förster,et al.  Discovery of Distant RR Lyrae Stars in the Milky Way Using DECam , 2018, 1802.01581.

[16]  R. Nichol,et al.  Stellar Streams Discovered in the Dark Energy Survey , 2018, The Astrophysical Journal.

[17]  Santi Cassisi,et al.  The ISLAnds Project. III. Variable Stars in Six Andromeda Dwarf Spheroidal Galaxies , 2017, 1710.09038.

[18]  A. Gautschy,et al.  On binary channels to anomalous Cepheids , 2017, 1704.00124.

[19]  S. Majewski,et al.  SMASH: Survey of the MAgellanic Stellar History , 2017, 1701.00502.

[20]  M. Irwin,et al.  THE PAndAS VIEW OF THE ANDROMEDA SATELLITE SYSTEM. II. DETAILED PROPERTIES OF 23 M31 DWARF SPHEROIDAL GALAXIES , 2016, 1610.01158.

[21]  P. McMillan,et al.  The mass distribution and gravitational potential of the Milky Way , 2016, 1608.00971.

[22]  G. Fiorentino,et al.  Variable stars in Local Group Galaxies - II. Sculptor dSph , 2016, 1607.08518.

[23]  Sergey E. Koposov,et al.  The feeble giant. Discovery of a large and diffuse Milky Way dwarf galaxy in the constellation of Crater , 2016, 1601.07178.

[24]  Abhijit Saha,et al.  VARIABLE STARS IN THE FIELD OF THE HYDRA II ULTRA-FAINT DWARF GALAXY , 2015, 1510.05539.

[25]  M. Catelán,et al.  Pulsating Stars: Smith/Pulsating Stars , 2015 .

[26]  V. Belokurov,et al.  `Skinny Milky Way please', says Sagittarius , 2014, 1406.2243.

[27]  Sergey E. Koposov,et al.  THE CATALINA SURVEYS PERIODIC VARIABLE STAR CATALOG , 2014, 1405.4290.

[28]  Andrew J. Connolly,et al.  Statistics, Data Mining, and Machine Learning in Astronomy , 2014 .

[29]  A. K. Vivas,et al.  A COMPREHENSIVE, WIDE-FIELD STUDY OF PULSATING STARS IN THE CARINA DWARF SPHEROIDAL GALAXY , 2013, 1309.2799.

[30]  V. Belokurov.  Galactic Archaeology. The dwarfs that survived and perished , 2013, 1307.0041.

[31]  R. Kudritzki,et al.  An eclipsing-binary distance to the Large Magellanic Cloud accurate to two per cent , 2013, Nature.

[32]  Alan W. McConnachie,et al.  THE OBSERVED PROPERTIES OF DWARF GALAXIES IN AND AROUND THE LOCAL GROUP , 2012, 1204.1562.

[33]  Giuliana Fiorentino,et al.  Anomalous Cepheids in the Large Magellanic Cloud - Insight into their origin and connection with the star formation history , 2012, 1202.2752.

[34]  Warren R. Brown,et al.  LOW-AMPLITUDE VARIABLES: DISTINGUISHING RR LYRAE STARS FROM ECLIPSING BINARIES , 2010, 1003.3656.

[35]  B. Willman.  In Pursuit of the Least Luminous Galaxies , 2009, 0907.4758.

[36]  K. Kinemuchi,et al.  THE VARIABLE STARS OF THE DRACO DWARF SPHEROIDAL GALAXY: REVISITED , 2008, 0808.2542.

[37]  M. Catelán,et al.  The Period-Luminosity Relation of RR Lyrae Stars in the SDSS Photometric System , 2008, 0805.3704.

[38]  B. Robertson,et al.  Are the Magellanic Clouds on Their First Passage about the Milky Way? , 2007, astro-ph/0703196.

[39]  M. Catelán.  Horizontal branch stars: the interplay between observations and theory, and insights into the formation of the Galaxy , 2005, astro-ph/0507464.

[40]  J.Lee,et al.  THE DARK ENERGY CAMERA , 2004, The Dark Energy Survey.

[41]  N. Suntzeff,et al.  New Understanding of Large Magellanic Cloud Structure, Dynamics, and Orbit from Carbon Star Kinematics , 2002, astro-ph/0205161.

[42]  D. Schlegel,et al.  Maps of Dust Infrared Emission for Use in Estimation of Reddening and Cosmic Microwave Background Radiation Foregrounds , 1998 .

[43]  J. Binney,et al.  Mass models of the Milky Way , 1996, astro-ph/9612059.

[44]  M. Mateo,et al.  Variable Stars in the Sextans Dwarf Spheroidal Galaxy , 1995 .

[45]  Peter B. Stetson,et al.  THE CENTER OF THE CORE-CUSP GLOBULAR CLUSTER M15: CFHT AND HST OBSERVATIONS, ALLFRAME REDUCTIONS , 1994 .

[46]  P. Stetson.  DAOPHOT: A COMPUTER PROGRAM FOR CROWDED-FIELD STELLAR PHOTOMETRY , 1987 .

[47]  Jean-Luc Starck,et al.  Astronomical Data Analysis , 2007 .