Observations of the evolution of HI in galaxies across different environments. D.J. Pisano (West Virginia University) Why study galaxy environment? • Nature vs. Nurture – Can they be distinguished? – What does the environment do to a galaxy? – What would a galaxy look like without any environmental influence? • Study phenomena that strongly depend on the environment. – cold mode accretion, tidal interactions, ram pressure stripping Physical Processes affecting HI content • Inflow – Gas accretion (cold mode, hot mode) – Minor/major interactions & mergers • Consumption (star formation) • Outflow – fly-by encounters, tidal stripping – ram-pressure stripping – AGN, SF feedback The importance of each process depends, in part, on environment. Physical Processes affecting HI content • Inflow – Gas accretion (cold mode, hot mode) – Minor/major interactions & mergers Galaxy Density ⇐low, high ⇐moderate • Consumption (star formation) • Outflow – fly-by encounters, tidal stripping – ram-pressure stripping – AGN, SF feedback ⇐high (clusters) ⇐moderate-high ⇐moderate-high, any The importance of each process depends, in part, on environment. Hot/Cold Flows • Many simulations predict that gas is accreted by galaxies in two forms (e.g. Birnboim & Dekel 2003, Keres et al. 2005, 2009). • At z=0, hot mode accretion should be dominant in high mass halos, and in high density environments. • Cold mode should be dominant for Mhalo ≤ 1011-12 M and in low density environments. • To find cold mode accretion, must search in low density environments. z=5.52 Green =cold z=3.24 Green =hot Keres et al. 2005 How do we define environment? Local Environment • Isolated – no companions brighter/more massive than a certain level within a given distance. • Galaxy pairs & triplets • Compact Groups – 4 or more galaxies within 3 mag of brightest galaxy. – no similar galaxies within 3 Rg – mean surface brightness < 26 mag/sq. arcsec (300108 Mpc-2) Global Environment • “Field” vs. Cluster • Voids vs. Filaments • Voids Groups (loose, poor, rich) Clusters • Groups can be within both voids and clusters. A galaxy has both a local & global environment. Both the local and global environment affect galaxy properties. HI properties vs. Global Environment A statistical look: • HI mass function • Circular velocity function (halo mass function). • HI mass fraction, distribution HI Mass Function Martin et al. 2010 • Similar global HIMF between ALFALFA & HIPASS • Low MHI slope flattens as density decreases. Zwaan et al. 2005 HIMF Freeland et al. 2009 Springob et al. 2005 • Springob et al. (2005) found that the slope flattens in Virgo core. • All other studies show flat low mass slope in groups (of varying densities). Kilborn et al. 2009 HIMF Martin et al. 2010 Pisano et al. 2011 • Similar global HIMF between ALFALFA & HIPASS • Pisano et al. (2011) found that Local Group analogs had flat low mass slope. Circular Velocity Function • Little evidence of variation with environment. • Slightly lower in underdense regions. Zwaan et al. 2010 Papastergis et al. 2011 Circular Velocity Function • Similar shape in groups as well (Pisano et al. 2011, confirmed by Abramson et al. 2014). • Desai et al. (2004) found clusters follow the expected CDM power law. HI mass fraction Fabello et al. 2012 • Based on HI stacking of ALFALFA data for GASS galaxies. • As Mgroup (N) increases, the HI mass fraction decreases. • Evidence for ram pressure stripping in moderate density environments. HI content in groups • Hess & Wilcots (2013) found that as N increases, radius of HI detections increases, implying removal of HI in groups. • Number of HI detections drops as group mass increases. • Kilborn et al. (2009) found that HI deficiency in groups increases with X-ray luminosity implying ram pressure stripping important in groups with X-ray IGM. Hess & Wilcots 2013 Kilborn et al. 2009 HI properties vs. environment • HI mass function appears to flatten as galaxy density drops. • Circular velocity (halo mass) function is unaffected by environment; only agrees with CDM predictions in clusters. • Decrease in fgas, Ndetections and increase in HI distribution in groups (with group mass) suggests ram pressure stripping is occurring even in moderate density environments. Local vs. Global Environment • Isolated vs. Void galaxies • Compact groups vs. Loose Groups • Different regions of Clusters Isolated Galaxies UGC 260 UGC 11152 29% (12/41) of isolated galaxies have companions or signatures of recent interaction/accretion. IC 5078 Total HI Intensity Contours on Optical 1,5,10,50,100 x 1019 cm-2. NGC 6368 Pisano et al. 2003 AMIGA Isolated Galaxies CIG 292 (Portas et al. 2011) CIG 340 (Scott et al. 2014) All of of the AMIGA isolated galaxies that have been mapped show signatures of interactions (maybe accretion?). Some of these are in small, low density groups. Only 2% of AMIGA HI profiles are “highly CIG 96 (Espada et al. 2005) CIG 85 (Sengupta et al. 2012) asymmetric” compared to 10-20% of field galaxies (Espada et al. 2011) Problem with Profiles HI distribution HI profile It is impossible to unambiguously find signatures of interactions, asymmetries, or a companion with just an HI profile. HI in void galaxies Of the 55 void galaxies imaged by Kreckel et al. (2012), about 50% have strongly disturbed HI morphology or kinematics. A much higher rate than seen in isolated galaxies. This suggests an ongoing interaction or accretion from the IGM. Kreckel et al. 2011, 2012 NGC 6946 • NGC 6946 is a void galaxy in a group. Local galaxy density is 0.07 Mpc-3 (Tully 1988) • Optical in blue, WSRT HI data in green, GBT HI data in red. • GBT can detect HI down to NHI = 1018 cm-2. • Filament has peak NHI = 2x1018 cm-2 and FWHM = 48 km/s. • The filament smoothly connects in position and velocity with NGC 6946 and companions. • Some emission from filament could be due to stray radiation. • Filament could be a cold flow, but is more likely to be a tidal stream. No visible stellar counterpart. Pisano (2014) Boomsma et al. (2008) NGC 2403 • A group galaxy with local galaxy density of 0.3 Mpc-3. • Fraternali et al. 2001 found an anomalous velocity HI cloud in their WSRT data. • Our GBT data (de Blok et al. 2014) reveal a more diffuse, extended cloud connected spatially and kinematically. • This may have a tidal or accretion origin. Compact Groups Verdes-Montenegro et al. 2001 • As group assembles, HI is removed from galaxies. • Either HI becomes diffuse envelope in group (e.g. Borthakur et al. 2010, Stevens et al. 2004), or turns into hot gas. • Interactions are very important. Loose groups • Loose groups are larger than compact groups (and could contain them). • NGC 2997 group (Pisano et al. 2011; left) is a Local Group analog. • USGC U451 group (Freeland et al. 2009; right) is a more massive X-ray bright group containing two compact groups (NGC 4076, 4098). HI at the 1017 cm-2 level in the Local Group NHI = 0.5 – 20 x 1018 cm-2 Thilker et al. 2004; Braun & Thilker 2004 But is this really diffuse? Wolfe et al. 2013 The GBT data shows that this feature is much clumpier than previous data suggested. We think that they are part of a condensing intergalactic filament. Cloud #4 may have a stellar counterpart (Martin et al. 2013) and appears to be interacting with a CGM or IGM.Wolfe et al. 2013 It is not associated with nearby dwarf galaxies. Wolfe et al. 2013 The clouds are at different velocities than M31’s HVCs and its dwarf companions, so they are a different phenomenon. VIVA observations of the Virgo Cluster • HI deficient galaxies in center of cluster. • Tidal interactions occur in outskirts of cluster. • Signs of ram-pressure stripping as galaxies pass through cluster. • More details in the next talk. Chung et al. 2009 Summary • Studying different environments sheds light on different physical processes. • A good definition of the environment is important as both local and global environment matter. • Void galaxies show more signatures of interaction/accretion than isolated galaxies. • Signatures of accretion present around galaxies in voids and low density groups. • Evidence for processing of HI through tidal interactions and ram pressure stripping in even moderate density groups. Future Work • What will surveys like WALLABY and MHONGOOSE reveal about HI across environments and at better sensitivity? • Can we find conclusive evidence for cold mode accretion in low density environments in future surveys?