EVIDENCE THAT HYDRA I IS A TIDALLY DISRUPTING MILKY WAY DWARF GALAXY

Jonathan R. Hargis; Brian Kimmig; Beth Willman; Nelson Caldwell; Matthew G. Walker; Jay Strader; David J. Sand; Carl J. Grillmair; Joo Heon Yoon

doi:10.3847/0004-637X/818/1/39

EVIDENCE THAT HYDRA I IS A TIDALLY DISRUPTING MILKY WAY DWARF GALAXY

Jonathan R. Hargis, Brian Kimmig, Beth Willman, Nelson Caldwell, Matthew G. Walker, Jay Strader, David J. Sand, Carl J. Grillmair, Joo Heon Yoon

Research output: Contribution to journal › Article › peer-review

6 Scopus citations

Abstract

The Eastern Banded Structure (EBS) and Hydra I halo overdensities are very nearby (d ∼ 10 kpc) objects discovered in Sloan Digital Sky Survey (SDSS) data. Previous studies of the region have shown that EBS and Hydra I are spatially coincident, cold structures at the same distance, suggesting that Hydra I may be the EBS's progenitor. We combine new wide-field Dark Energy Camera (DECam) imaging and MMT/Hectochelle spectroscopic observations of Hydra I with SDSS archival spectroscopic observations to quantify Hydra I's present-day chemodynamical properties, and to infer whether it originated as a star cluster or dwarf galaxy. While previous work using shallow SDSS imaging assumed a standard old, metal-poor stellar population, our deeper DECam imaging reveals that Hydra I has a thin, well-defined main sequence turnoff of intermediate age (∼5-6 Gyr) and metallicity ([Fe/H] = -0.9 dex). We measure statistically significant spreads in both the iron and alpha-element abundances of ^σ[Fe/H] = 0.13 ± 0.02 dex and ^σ[/Fe] = 0.09 ± 0.03 and dex, respectively, and place upper limits on both the rotation and its proper motion. Hydra I's intermediate age and [Fe/H] - as well as its low [/Fe], apparent [Fe/H] spread, and present-day low luminosity - suggest that its progenitor was a dwarf galaxy, which has subsequently lost more than 99.99% of its stellar mass.

Original language	English (US)
Article number	39
Journal	Astrophysical Journal
Volume	818
Issue number	1
DOIs	https://doi.org/10.3847/0004-637X/818/1/39
State	Published - Feb 10 2016
Externally published	Yes

Keywords

Galaxy: halo
Galaxy: structure
galaxies: dwarf

ASJC Scopus subject areas

Astronomy and Astrophysics
Space and Planetary Science

Access to Document

10.3847/0004-637X/818/1/39

Cite this

@article{056b331217a9493f93204bffd1ed9332,

title = "EVIDENCE THAT HYDRA I IS A TIDALLY DISRUPTING MILKY WAY DWARF GALAXY",

abstract = "The Eastern Banded Structure (EBS) and Hydra I halo overdensities are very nearby (d ∼ 10 kpc) objects discovered in Sloan Digital Sky Survey (SDSS) data. Previous studies of the region have shown that EBS and Hydra I are spatially coincident, cold structures at the same distance, suggesting that Hydra I may be the EBS's progenitor. We combine new wide-field Dark Energy Camera (DECam) imaging and MMT/Hectochelle spectroscopic observations of Hydra I with SDSS archival spectroscopic observations to quantify Hydra I's present-day chemodynamical properties, and to infer whether it originated as a star cluster or dwarf galaxy. While previous work using shallow SDSS imaging assumed a standard old, metal-poor stellar population, our deeper DECam imaging reveals that Hydra I has a thin, well-defined main sequence turnoff of intermediate age (∼5-6 Gyr) and metallicity ([Fe/H] = -0.9 dex). We measure statistically significant spreads in both the iron and alpha-element abundances of σ[Fe/H] = 0.13 ± 0.02 dex and σ[/Fe] = 0.09 ± 0.03 and dex, respectively, and place upper limits on both the rotation and its proper motion. Hydra I's intermediate age and [Fe/H] - as well as its low [/Fe], apparent [Fe/H] spread, and present-day low luminosity - suggest that its progenitor was a dwarf galaxy, which has subsequently lost more than 99.99% of its stellar mass.",

keywords = "Galaxy: halo, Galaxy: structure, galaxies: dwarf",

author = "Hargis, {Jonathan R.} and Brian Kimmig and Beth Willman and Nelson Caldwell and Walker, {Matthew G.} and Jay Strader and Sand, {David J.} and Grillmair, {Carl J.} and Yoon, {Joo Heon}",

note = "Funding Information: B.W., J.R.H., and B.K. were supported by an NSF Faculty Early Career Development (CAREER) award (AST-1151462). M.G.W. is supported by National Science Foundation grants AST-1313045, AST-1412999. J.S. acknowledges support from NSF grant AST-1514763. J.R.H. would like to acknowledge useful conversations with Keith Hawkins, Ting Li, and Jennifer Marshall during the course of this work. J.R.H. would also like to thank Kathy Vivas both for useful conversations and observing support during the DECam observing at CTIO. We thank the anonymous referee for very helpful comments on the manuscript. This work was supported in part by National Science Foundation Grant No. PHYS-1066293 and the hospitality of the Aspen Center for Physics. This project used data obtained with the Dark Energy Camera, which was constructed by the Dark Energy Survey collaboration. Funding for the DES Projects has been provided by the DOE and NSF (USA), MISE(Spain), STFC(UK), HEFCE(UK). NCSA (UIUC), KICP(U. Chicago), CCAPP(Ohio State), MIFPA (Texas A&M), CNPQ, FAPERJ, FINEP (Brazil), MINECO (Spain), DFG(Germany) and the collaborating institutions in the Dark Energy Survey, which are Argonne Lab, UC Santa Cruz, University of Cambridge, CIEMAT-Madrid, University of Chicago, University College London, DES-Brazil Consortium, University of Edinburgh, ETH Zurich, Fermilab, University of Illinois, ICE (IEEC-CSIC), IFAE Barcelona, Lawrence Berkeley Lab, LMU Munchen and the associated Excellence Cluster universe, University of Michigan, NOAO, University of Nottingham, Ohio State University, University of Pennsylvania, University of Portsmouth, SLAC National Lab, Stanford University, University of Sussex, and Texas A&M University. Publisher Copyright: {\textcopyright} 2016. The American Astronomical Society. All rights reserved.",

year = "2016",

month = feb,

day = "10",

doi = "10.3847/0004-637X/818/1/39",

language = "English (US)",

volume = "818",

journal = "Astrophysical Journal",

issn = "0004-637X",

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TY - JOUR

T1 - EVIDENCE THAT HYDRA I IS A TIDALLY DISRUPTING MILKY WAY DWARF GALAXY

AU - Hargis, Jonathan R.

AU - Kimmig, Brian

AU - Willman, Beth

AU - Caldwell, Nelson

AU - Walker, Matthew G.

AU - Strader, Jay

AU - Sand, David J.

AU - Grillmair, Carl J.

AU - Yoon, Joo Heon

N1 - Funding Information: B.W., J.R.H., and B.K. were supported by an NSF Faculty Early Career Development (CAREER) award (AST-1151462). M.G.W. is supported by National Science Foundation grants AST-1313045, AST-1412999. J.S. acknowledges support from NSF grant AST-1514763. J.R.H. would like to acknowledge useful conversations with Keith Hawkins, Ting Li, and Jennifer Marshall during the course of this work. J.R.H. would also like to thank Kathy Vivas both for useful conversations and observing support during the DECam observing at CTIO. We thank the anonymous referee for very helpful comments on the manuscript. This work was supported in part by National Science Foundation Grant No. PHYS-1066293 and the hospitality of the Aspen Center for Physics. This project used data obtained with the Dark Energy Camera, which was constructed by the Dark Energy Survey collaboration. Funding for the DES Projects has been provided by the DOE and NSF (USA), MISE(Spain), STFC(UK), HEFCE(UK). NCSA (UIUC), KICP(U. Chicago), CCAPP(Ohio State), MIFPA (Texas A&M), CNPQ, FAPERJ, FINEP (Brazil), MINECO (Spain), DFG(Germany) and the collaborating institutions in the Dark Energy Survey, which are Argonne Lab, UC Santa Cruz, University of Cambridge, CIEMAT-Madrid, University of Chicago, University College London, DES-Brazil Consortium, University of Edinburgh, ETH Zurich, Fermilab, University of Illinois, ICE (IEEC-CSIC), IFAE Barcelona, Lawrence Berkeley Lab, LMU Munchen and the associated Excellence Cluster universe, University of Michigan, NOAO, University of Nottingham, Ohio State University, University of Pennsylvania, University of Portsmouth, SLAC National Lab, Stanford University, University of Sussex, and Texas A&M University. Publisher Copyright: © 2016. The American Astronomical Society. All rights reserved.

PY - 2016/2/10

Y1 - 2016/2/10

N2 - The Eastern Banded Structure (EBS) and Hydra I halo overdensities are very nearby (d ∼ 10 kpc) objects discovered in Sloan Digital Sky Survey (SDSS) data. Previous studies of the region have shown that EBS and Hydra I are spatially coincident, cold structures at the same distance, suggesting that Hydra I may be the EBS's progenitor. We combine new wide-field Dark Energy Camera (DECam) imaging and MMT/Hectochelle spectroscopic observations of Hydra I with SDSS archival spectroscopic observations to quantify Hydra I's present-day chemodynamical properties, and to infer whether it originated as a star cluster or dwarf galaxy. While previous work using shallow SDSS imaging assumed a standard old, metal-poor stellar population, our deeper DECam imaging reveals that Hydra I has a thin, well-defined main sequence turnoff of intermediate age (∼5-6 Gyr) and metallicity ([Fe/H] = -0.9 dex). We measure statistically significant spreads in both the iron and alpha-element abundances of σ[Fe/H] = 0.13 ± 0.02 dex and σ[/Fe] = 0.09 ± 0.03 and dex, respectively, and place upper limits on both the rotation and its proper motion. Hydra I's intermediate age and [Fe/H] - as well as its low [/Fe], apparent [Fe/H] spread, and present-day low luminosity - suggest that its progenitor was a dwarf galaxy, which has subsequently lost more than 99.99% of its stellar mass.

AB - The Eastern Banded Structure (EBS) and Hydra I halo overdensities are very nearby (d ∼ 10 kpc) objects discovered in Sloan Digital Sky Survey (SDSS) data. Previous studies of the region have shown that EBS and Hydra I are spatially coincident, cold structures at the same distance, suggesting that Hydra I may be the EBS's progenitor. We combine new wide-field Dark Energy Camera (DECam) imaging and MMT/Hectochelle spectroscopic observations of Hydra I with SDSS archival spectroscopic observations to quantify Hydra I's present-day chemodynamical properties, and to infer whether it originated as a star cluster or dwarf galaxy. While previous work using shallow SDSS imaging assumed a standard old, metal-poor stellar population, our deeper DECam imaging reveals that Hydra I has a thin, well-defined main sequence turnoff of intermediate age (∼5-6 Gyr) and metallicity ([Fe/H] = -0.9 dex). We measure statistically significant spreads in both the iron and alpha-element abundances of σ[Fe/H] = 0.13 ± 0.02 dex and σ[/Fe] = 0.09 ± 0.03 and dex, respectively, and place upper limits on both the rotation and its proper motion. Hydra I's intermediate age and [Fe/H] - as well as its low [/Fe], apparent [Fe/H] spread, and present-day low luminosity - suggest that its progenitor was a dwarf galaxy, which has subsequently lost more than 99.99% of its stellar mass.

KW - Galaxy: halo

KW - Galaxy: structure

KW - galaxies: dwarf

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U2 - 10.3847/0004-637X/818/1/39

DO - 10.3847/0004-637X/818/1/39

M3 - Article

AN - SCOPUS:84959079573

SN - 0004-637X

VL - 818

JO - Astrophysical Journal

JF - Astrophysical Journal

IS - 1

M1 - 39

ER -

EVIDENCE THAT HYDRA I IS A TIDALLY DISRUPTING MILKY WAY DWARF GALAXY

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EVIDENCE THAT HYDRA I IS A TIDALLY DISRUPTING MILKY WAY DWARF GALAXY

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ASJC Scopus subject areas

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Hydra I wide-field imaging and spectroscopy obs.

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