A comprehensive view of the Virgo stellar stream

Abstract

To explore the complex halo substructure that has been reported in the direction of the Virgo constellation, radial velocities and metallicities have been measured for 82 RR Lyrae stars (RRLS) that were identified by the QUEST survey. These stars are distributed over 90 square degrees of the sky, and lie from 4 to 23 kpc from the Sun. Using an algorithm for finding groups in phase space and modeling the smooth halo component in the region, we identified the 5 most significant RRLS groups, some of which were previously known or suspected. We have examined the SEKBO and the Catalina catalog of RRLS (with available spectroscopic measurements), as well as the bright QUEST RRLS sample, the catalog of Red Giant stars from the Spaghetti survey, and three recent catalogs of blue horizontal branch (BHB) stars, for stars that may be related to the QUEST RRLS groups. The most significant group of RRLS is the Virgo stellar stream (VSS) identified here as group A, which is composed of at least 10 RRLS and 3 BHB stars. It has a mean distance of 19.6 kpc and a mean radial velocity V gsr = 128 km s −1 , as estimated from its RRLS members. With the revised velocities reported here, there is no longer an offset in velocity between the RRLS in the VSS and the prominent peak in the velocities of main-sequence turnoff stars reported by other researchers in the same direction and at a similar distance (known as S297+63-20.5). The location in phase space of two other groups (F and H) suggests a possible connection with the VSS, which cannot be discarded at this point, although the turnoff colors of the VSS and group H, as identified from other works, suggest they might be composed of different populations. Two more groups, B and D, are found at mean distances of 19.0 and 5.7 kpc, and mean radial velocities of V gsr = −94 and 32 km s −1 . The latter is the more numerous in terms of total members, as well as the more extended in RA. A comparison with the latest model of the disruption of the Sagittarius dwarf, indicates that none of the above groups is related to it. Rather than being the result of a single accretion event, the excess of stars observed in Virgo appears to be composed of several halo substructures along the same line of sight.

Disentangling the Virgo Overdensity With Rr Lyrae Stars

“…For example, using deep photometry, Jerjen et al (2013) identified a main sequence population at 23 kpc near the center of the VOD. They did not find clear evidence of a population at 19 kpc, which is where the main overdensity of RR Lyrae stars (RRLS) is located Duffau et al 2014). Similarly, Brink et al (2010) found a peak in the velocity distribution of main sequence stars which is not coincident with the main peaks found by Newberg et al (2007) using F-turnoff stars and by Duffau et al (2006Duffau et al ( , 2014 using RRLS.…”

“…They did not find clear evidence of a population at 19 kpc, which is where the main overdensity of RR Lyrae stars (RRLS) is located Duffau et al 2014). Similarly, Brink et al (2010) found a peak in the velocity distribution of main sequence stars which is not coincident with the main peaks found by Newberg et al (2007) using F-turnoff stars and by Duffau et al (2006Duffau et al ( , 2014 using RRLS. Both the works of Brink et al (2010) and Jerjen et al (2013) were based in detailed studies of very small regions (of the order of arcmin) in an overdensity which covers a few thousand of square degrees.…”

“…In both cases the interpretation of an extra-galactic origin for these features is not clear and their possible relationship with the galactic disk is still under investigation (see Price-Whelan et al 2015;Xu et al 2015). At high galactic latitudes and far from the disk, there are several other structures: the Virgo overdensity (VOD, Vivas et al 2001;Newberg et al 2002;Duffau et al 2006;Jurić et al 2008;Bonaca et al 2012;Duffau et al 2014), the Hercules-Aquila cloud (Belokurov et al 2007;Watkins et al 2009;Simion et al 2014), the Pisces overdensity (Sesar et al 2007;Watkins et al 2009;Kollmeier et al 2009;Sesar et al 2010) and the Eridanus-Phoenix overdensity (Li et al 2016). Although their interpretation as merger event, or events, is less ambiguous, the specific merging history is still unknown.…”

The Next Generation Virgo Cluster Survey. Xix. Tomography of Milky Way Substructures in the NGVS Footprint

“…The VOD is now recognized to span more than 1000 square degrees (Jurić et al 2008;Jerjen et al 2013) and contain several dense clumps embedded within it (Vivas et al 2001;Newberg et al 2002Newberg et al , 2007Vivas & Zinn 2003, 2006Keller et al 2008Keller et al , 2009Keller et al , 2010. In addition to the large-scale excess of halo stars that was originally used to identify the VOD, several distinct, kinematically grouped substructures have now been found in this region (Duffau et al 2006(Duffau et al , 2010(Duffau et al , 2014Newberg et al 2007;Vivas et al 2008;Prior et al 2009;Starkenburg et al 2009;Brink et al 2010;Casey et al 2012). Although most of these kinematical structures show high positive galactocentric velocities, their spread in velocity can be more than 100 km s −1 .…”

New tidal debris nearby the Sagittarius leading tail from the LAMOST DR2 M giant stars

“…• well overlap with the RR Lyrae substructure discovered by Duffau et al (2014). At the other end, the region of 200…”