Substructure revealed by RR Lyraes in SDSS Stripe 82

By L. Watkins, N. Evans II, V. Belokurov, M. Smith, Paul Hewett, D. Bramich, G. Gilmore, M. Irwin, S. Vidrih, L. Wyrzykowski and 5 more. 2009

217 citations recorded by the source corpus.

We present an analysis of the substructure revealed by RR Lyraes in Sloan Digital Sky Survey Stripe 82, which covers 2°5 in declination on the celestial equator over the right ascension range α = 20 h .7 to 3 h .3. We use the new public archive of light-motion curves in Stripe 82, published by Bramich et al. in 2008, to identify a set of high-quality RR Lyrae candidates. Period estimates are determined to high accuracy using a string-length method. A subset of 178 RR Lyraes with spectrally derived metallicities are employed to derive metallicity-period-amplitude relations, which are then used, together with archive magnitude data and light-curve Fourier decomposition, to estimate metallicities and hence distances for the entire sample. The RR Lyraes lie 5-115 kpc from the Galactic Centre, with distance estimates accurate to ∼8 per cent. The RR Lyraes are further divided into subsets of 316 RRab types and 91 RRc types based on their period, colour and metallicity. We fit a smooth density law to the distribution as a simple representation of the data. For Galactocentric radii 5-25 kpc the number density of RR Lyraes falls as r ―2,4 , but beyond 25 kpc, the number density falls much more steeply, as r ―4.5 . However, we stress that in practice the density distribution is not smooth, but dominated by clumps and substructure. Samples of 55 and 237 RR Lyraes associated with the Sagittarius Stream and the Hercules-Aquila Cloud, respectively, are identified. Hence, ∼70 per cent of the RR Lyraes in Stripe 82 belong to known substructure, and the sharp break in the density law reflects the fact that the dominant substructure in Stripe 82 - the Hercules-Aquila Cloud and the Sagittarius Stream -lie within 40 kpc. In fact, almost 60 per cent of all the RR Lyraes in Stripe 82 are associated with the Hercules-Aquila Cloud alone, which emphasizes the cloud's pre-eminence. Additionally, evidence of a new and distant substructure - the Pisces Overdensity ― is found, consisting of 28 faint RRLyraes centred on Galactic coordinates (l ≈ 80°, b ≈ -55°), with distances of ∼80 kpc. The total stellar mass in the Pisces Overdensity is ∼10 4 M ⊙ and its metallicity is [Fe/H]∼ ―1.5.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/b90f3151c54afa8215fbaf11959afa76faef2522

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Citations in the corpus

THE SAGITTARIUS DWARF GALAXY: A MODEL FOR EVOLUTION IN A TRIAXIAL MILKY WAY HALO (2010, methodology): “The radial velocity of a sample of RRL in Stripe 82 has recently been measured by Watkins et al. (2009), who detect a component with vGSR = −130 km s−1 , which is matched by the mean radial velocity of the T1 stream at this position to within 5 km s−1 .”
The Milky Way's rotation curve out to 100 kpc and its constraint on the Galactic mass distribution (2016, methodology): “Similar to Kafle et al. (2014), here we adopt a spherical (i.e.q = 1), broken power-law distribution for the stellar halo, assumingα = 2.4 for the inner halo (r 6 rb) and α = 4.5 for the outer halo (r > rb) from Watkins et al. (2009).”
Local-Group tests of dark-matter concordance cosmology - Towards a new paradigm for structure formation (2010, background): “Watkins et al. (2009) and Belokurov et al. (2010) reported the discovery of two new MW satellite galaxies, Pisces I and II, respectively, enlarging the total MW satellite system to 24 satellites.”
LIGHT CURVE TEMPLATES AND GALACTIC DISTRIBUTION OF RR LYRAE STARS FROM SLOAN DIGITAL SKY SURVEY STRIPE 82 (2009, methodology): “While this paper was in preparation, another study of RR Lyrae stars in stripe 82, based on essentially the same data set, was announced (Watkins et al. 2009).”
The formation and assembly history of the Milky Way revealed by its globular cluster population (2018, background): “Deason et al. (2013, also see Pillepich et al. 2014) suggest that the break in the density profile of the Galactic stellar halo at R ∼ 25 kpc (e.g. Watkins et al. 2009; Sesar et al. 2011) indicates an accretion event some 6–9 Gyr ago (corresponding to z = 0.6–1.3) of a single satellite that was…”
The biggest splash (2019, background): “…forward the hypothesis that the rapid transition in the Galactic stellar halo structural properties at the so-called break radius of 20–30 kpc (see Watkins et al. 2009; Deason, Belokurov & Evans 2011; Sesar, Jurić & Ivezić 2011) is due to the apocentre pile-up of the tidal debris from a small…”
BIG FISH, LITTLE FISH: TWO NEW ULTRA-FAINT SATELLITES OF THE MILKY WAY (2010, background): “The extent of Pisces I is probably considerable, at least as judged from the RR Lyrae populations (see Figure 12 of Watkins et al. 2009).”
The Milky Way stellar halo out to 40 kpc: squashed, broken but smooth (2011, methodology): “The distance to the stream in the right ascension range25◦ < α◦ < 40◦ was estimated by Watkins et al. (2009) using RR Lyrae stars as DSgr = 26.1± 5.6 kpc.”
Kinematics of SDSS subdwarfs: structure and substructure of the Milky Way halo (2009, background): “For example, Watkins et al. (2009) isolated the RR Lyrae variables by a combination of colour, metallicity and period cuts.”
ON THE SHOULDERS OF GIANTS: PROPERTIES OF THE STELLAR HALO AND THE MILKY WAY MASS DISTRIBUTION (2014, methodology): “Our estimates for the break radius is slightly smaller than∼ 27 kpc as claimed in Deason et al. (2011) or∼ 25 kpc as found in Watkins et al. (2009).”
Galactic stellar haloes in the CDM model (2009, background): “…by University of Groningen user on 17 April 2018 diffuse overdensities (Jurić et al. 2008; Belokurov et al. 2007a; Watkins et al. 2009), the Monoceros ‘ring’ (Newberg et al. 2002; Ibata et al. 2003; Yanny et al. 2003), the orphan stream (Belokurov et al. 2007b)…”
A BARYONIC SOLUTION TO THE MISSING SATELLITES PROBLEM (2012, background): “…et al. 2005; Irwin et al. 2007; Liu et al. 2008; Martin et al. 2008; Simon & Geha 2007; Grebel 2000; van den Bergh 2000; Belokurov et al. 2008; Watkins et al. 2009; Belokurov et al. 2010), there remains a considerable discrepancy between the number of observed MW satellites and the number…”
THE LARGE-SCALE STRUCTURE OF THE HALO OF THE ANDROMEDA GALAXY. I. GLOBAL STELLAR DENSITY, MORPHOLOGY AND METALLICITY PROPERTIES (2013, background): “In the Milky Way several studies have shown evidence for a break in the halo profile: this is seen in RRLyrae stars at a Galactocentric distance of ∼ 25 kpc (Watkins et al. 2009), in main sequence turn-off stars at ∼ 28 kpc (Sesar et al. 2011), and in BHB stars at 27 kpc (Deason et al. 2011).”
The Sausage Globular Clusters (2018, background): “For example, the radial density profile of the stellar halo shows a dramatic break at around 30 kpc in tracers such as RR Lyrae and blue horizontal branch stars (e.g., Watkins et al. 2009; Deason et al. 2011).”
THE CASE FOR THE DUAL HALO OF THE MILKY WAY (2011, background): “Both Watkins et al. (2009) and Sesar et al. (2010) have argued persuasively that single power-law profiles are incapable of describing the spatial variation of the halo system.”
MAPPING THE STELLAR STRUCTURE OF THE MILKY WAY THICK DISK AND HALO USING SEGUE PHOTOMETRY (2009, methodology): “Similarly, Watkins et al. (2009) use RR Lyrae variable stars in SDSS Stripe 82 to infer nh=−2.4 within 23 kpc and nh=−4.5 at larger distances.”
PROBING THE OUTER GALACTIC HALO WITH RR LYRAE FROM THE CATALINA SURVEYS (2012, methodology): “However, the Galactic halo itself has only been probed with confirmed RRL over a few thousand square degrees to heliocentric distances of ∼ 30 to 100 kpc (eg., Vivas et al. 2004; Keller et al. 2008; Miceli et al. 2008; Watkins et al. 2009; Sesar et al. 2010).”
KINEMATICS OF THE STELLAR HALO AND THE MASS DISTRIBUTION OF THE MILKY WAY USING BLUE HORIZONTAL BRANCH STARS (2012, methodology): “The only assumption that we make here is about the density profile which we choose to beα = 4.5 in consent to the recent results by Watkins et al. (2009); Deason et al. (2011b).”