J/ApJ/902/106ivo://CDS.VizieR/J/ApJ/902/106doi:10.26093/cds/vizier.19020106CDSMutlu-Pakdil B.Sand D.J.Crnojevic D.Olszewski E.W.,Zaritsky D.Strader J.Collins M.L.Seth A.C.Willman B.2022-10-26T11:03:00Z2022-05-10T12:45:21ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frgalaxiesphotometryhst-photometryproper-motionsextinctioninfrared-photometryvisible-astronomyThe ultrafaint dwarf galaxy Hercules has an extremely elongated morphology with both photometric overdensities and kinematic members at large radii, suggesting that it may be tidally disrupting due to a previous close encounter with the Milky Way. To explain its observational peculiarities, we present a deep Hubble Space Telescope (HST) imaging study of Hercules and its surrounding regions and investigate its tidal history through a careful search for a distance gradient along its stretched body. Our off-center HST data clearly resolve a main sequence, showing that the stellar extension seen along the major axis of Hercules is genuine, not a clump of background galaxies. Utilizing Gaia DR2 data, we clean the region around the Hercules of field contamination, and find four new plausible member stars, all of which are located on the outskirts of the dwarf galaxy. We update the distance to Hercules, and find 130.6R+/-6.1kpc (m-M=20.58+/-0.10) for the main body, which is consistent with earlier estimates in the literature. While we find no conclusive evidence for a distance gradient, our work demonstrates that constraining a distance gradient in such a faint system is not trivial, and the possible thickness of the dwarf along the line of sight and field contamination make it harder to make decisive conclusions even with these high-precision data. Future studies coupled with tailored theoretical models are needed to understand the true nature of Hercules and of tidal distortion observables in ultrafaint galaxies in general.2020ApJ...902..106Mhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/902/106CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toI/345 : Gaia DR2 (Gaia Collaboration, 2018)J/AJ/129/2714 : JHK photometry of M92 variable stars (Del Principe+, 2005)J/MNRAS/397/1748 : Spectroscopic study of Segue 2 (Belokurov+, 2009)J/ApJ/704/898 : Photometry of the Hercules dwarf galaxy (Sand+, 2009)J/AJ/142/22 : Heavy-element dispersion in M92 (Roederer+, 2011)J/ApJ/756/121 : Variable stars in Her dwarf galaxy (Musella+, 2012)J/ApJ/756/79 : Optical phot. in 3 Local Group dwarf galaxies (Sand+, 2012)J/ApJ/770/16 : Spectroscopic members of Segue 2 galaxy (Kirby+, 2013)J/A+A/570/A61 : PM-selected stars of Hercules galaxy (Fabrizio+, 2014)J/ApJ/866/22 : Spectroscopic analysis of Tuc III stream (Li+, 2018)J/ApJ/863/25 : Deep Magellan obs. of 4 MW satellites (Mutlu-Pakdil+, 2018)J/ApJ/863/89 : Gaia DR2 PMs of stars in MW satellites (Simon, 2018)J/ApJ/883/11 : Magellan/IMACS spectra of Crater II & Hercules (Fu+, 2019)J/ApJ/885/53 : Spectrosc. & HST phot. of galaxy Leo V (Mutlu-Pakdil+, 2019)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/902/106https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/902/106http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/902/106https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/902/106https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/902/106http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/902/106GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/902/106/table2 (Photometry of Hercules fields)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/902/106/table2?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/902/106/table2?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/902/106/table2?GETtext/xml+votable180.050000true247.7962612.78809610.005555555555555556Cone search capability for table J/ApJ/902/106/table4 (A clean members catalog for Hercules within our HST footprint)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/902/106/table4?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/902/106/table4?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/902/106/table4?GETtext/xml+votable180.050000true247.8086212.75738610.005555555555555556Cone search capability for table J/ApJ/902/106/table5 (List of plausible Hercules members, requiring further follow-up)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/902/106/table5?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/902/106/table5?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/902/106/table5?GETtext/xml+votable180.050000true247.6022312.87309110.0055555555555555566/316922.0401237512456292e-19 3.9057996558789745e-19https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/902/106?format=asciiOpticalInfrareddefaultJ/ApJ/902/106/table2Photometry of Hercules fieldsFieldField Nameobs.fieldcharF814W[18.07/28.93] F814W band magnitude in Cameramagphot.mag;em.opt.Ifloate_F814W[0.001/0.3] Uncertainty (DOLPHOT) in F814Wmagstat.errorfloatAF814W[0.08/0.1] Galactic extinction correction in F814Wmagphys.absorptionfloatS09Display data from Sand+, 2009, J/ApJ/704/898 within 0.5"meta.ref.urlintnullablerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintCamCamera used ("ACS" or "WFC3")meta.id;instrcharMClean Hercules member (link to Table 4)meta.ref.urlintnullableSeq[0/6435] Sequential identifier in Field/Camera subsetmeta.id;meta.mainintpMPlausible Hercules member (link to Table 5)meta.ref.urlintnullableRAJ2000[247.5/248] Right Ascension (J2000)degpos.eq.ra;meta.mainindexedDEJ2000[12.6/12.9] Declination (J2000)degpos.eq.dec;meta.mainindexedF606W[19.22/29.75] HST F606W band magnitude in Cameramagphot.mag;em.opt.Rfloate_F606W[0.001/0.3] Uncertainty (DOLPHOT) in F606Wmagstat.errorfloatAF606W[0.13/0.16] Galactic extinction correction in F606Wmagphys.absorptionfloatJ/ApJ/902/106/table4A clean members catalog for Hercules within our HST footprintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSeq[1/37] Assigned number for each starmeta.id;meta.mainintRAJ2000[247.5/248] Right Ascension (J2000)degpos.eq.ra;meta.mainDEJ2000[12.7/12.9] Declination (J2000)degpos.eq.dec;meta.mainF606W[19.17/22.11] HST F606W band magnitude in Camera/Filter catalogmagphot.mag;em.opt.RfloatF814W[18.3/22.1] HST F814W band magnitude in Camera/Filter catalogmagphot.mag;em.opt.IfloatpmRA[-1.6/0.6]? Gaia DR2 proper motion in RAmas/yrpos.pm;pos.eq.rafloatnullablee_pmRA[0.3/1.8]? Uncertainty in pmRAmas/yrstat.error;pos.pm;pos.eq.rafloatnullablepmDE[-2.2/1]? Gaia DR2 proper motion in DECmas/yrpos.pm;pos.eq.decfloatnullablee_pmDE[0.27/1.6]? Uncertainty in pmDEmas/yrstat.error;pos.pm;pos.eq.decfloatnullableFieldField Nameobs.fieldcharGaiaDisplay the Gaia DR2 data (I/345) within 3"meta.ref.urlcharRefReferences (1)meta.refcharJ/ApJ/902/106/table5List of plausible Hercules members, requiring further follow-uprecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintFieldField Nameobs.fieldcharRAJ2000[247.6/247.9] Right Ascension (J2000)degpos.eq.ra;meta.mainDEJ2000[12.6/12.9] Declination (J2000)degpos.eq.dec;meta.mainF606W[19.8/20.71] HST/ACS F606W band magnitude in Camera/Filter catalogmagphot.mag;em.opt.RfloatF814W[19/20.3] HST/ACS F814W band magnitude in Camera/Filter catalogmagphot.mag;em.opt.IfloatpmRA[-1.3/-0.2] Gaia DR2 proper motion in RAmas/yrpos.pm;pos.eq.rafloate_pmRA[0.6/2.4] Uncertainty in pmRAmas/yrstat.error;pos.pm;pos.eq.rafloatpmDE[-1.7/-0.27] Gaia DR2 proper motion in DECmas/yrpos.pm;pos.eq.decfloate_pmDE[0.5/2] Uncertainty in pmDEmas/yrstat.error;pos.pm;pos.eq.decfloatTypePosition on CMD (1)src.classcharPhotDisplay the photometry data (link to Table 2)meta.ref.urlcharGaiaDisplay the Gaia DR2 data (I/345) within 3"meta.ref.urlchar