Systemic proper motions of milky way satellites from stellar redshifts: the carina, fornax, sculptor, and sextans dwarf spheroidals

Matthew G. Walker, Mario Mateo, Edward W Olszewski

Research output: Contribution to journalArticle

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Abstract

The transverse motions of nearby dwarf spheroidal (dSph) galaxies contribute line-of-sight components that increase with angular distance from the dSph centers, inducing detectable gradients in stellar redshift. In the absence of an intrinsic velocity gradient (e.g., due to rotation or streaming), an observed gradient in the heliocentric rest frame (HRF) relates simply to a dSph's systemic proper motion (PM). Kinematic samples for the Milky Way's brightest dSph satellites are now sufficiently large that we can use stellar redshifts to constrain systemic PMs independently of astrometric data. Data from our Michigan/MIKE Fiber System (MMFS) Survey reveal significant HRF velocity gradients in Carina, Fornax, and Sculptor, and no significant gradient in Sextans. Assuming there are no intrinsic gradients, the data provide a relatively tight constraint on the PM of Fornax, (μHRF α, μHRFdelta;)=(+48 ± 15,-25 ± 14) mas century-1, that agrees with published HST astrometric measurements. Smaller data sets yield weaker constraints in the remaining galaxies, but our Carina measurement, (μHRF α, μHRFdelta;)=(+25 ± 36, +16 ± 43) mas century-1, agrees with the published astrometric value. The disagreement of our Sculptor measurement, (μHRF α, μHRFdelta;)=(-40 ± 29,-69 ± 47) mas century-1, with astrometric measurements is expected if Sculptor has a rotational component as reported by Battaglia and coworkers. For Sextans, which at present lacks an astrometric measurement, we measure (μHRFα, μHRFdelta;)=(-26 ± 41, +10 ± 44) mas century-1.

Original languageEnglish (US)
JournalAstrophysical Journal
Volume687
Issue number2 PART 2
DOIs
StatePublished - 2008

Fingerprint

proper motion
gradients
kinematics
dwarf galaxies
line of sight
galaxies
fibers

Keywords

  • Galaxies: Dwarf
  • Galaxies: Individual (Carina, Fornax, Sculptor, Sextans)
  • Local group

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Systemic proper motions of milky way satellites from stellar redshifts : the carina, fornax, sculptor, and sextans dwarf spheroidals. / Walker, Matthew G.; Mateo, Mario; Olszewski, Edward W.

In: Astrophysical Journal, Vol. 687, No. 2 PART 2, 2008.

Research output: Contribution to journalArticle

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