Observations of the evolution of HI in galaxies across different
environments. D.J. Pisano (West Virginia University) Slide 2 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 Slide 3
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. Slide 4 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. Galaxy Density low, high moderate high
(clusters) moderate-high moderate-high, any Slide 5 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 M
halo 10 11-12 M and in low density environments. To find cold mode
accretion, must search in low density environments. Keres et al.
2005 z=5.52 z=3.24 Green =cold Green =hot Slide 6 How do we define
environment? Slide 7 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 R g
mean surface brightness < 26 mag/sq. arcsec (300- 10 8 Mpc -2 )
Slide 8 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. Slide 9 HI properties vs. Global Environment A
statistical look: HI mass function Circular velocity function (halo
mass function). HI mass fraction, distribution Slide 10 HI Mass
Function Similar global HIMF between ALFALFA & HIPASS Low M HI
slope flattens as density decreases. Martin et al. 2010 Zwaan et
al. 2005 Slide 11 HIMF 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). Springob et al. 2005 Freeland et
al. 2009 Kilborn et al. 2009 Slide 12 HIMF Similar global HIMF
between ALFALFA & HIPASS Pisano et al. (2011) found that Local
Group analogs had flat low mass slope. Martin et al. 2010 Pisano et
al. 2011 Slide 13 Circular Velocity Function Little evidence of
variation with environment. Slightly lower in underdense regions.
Papastergis et al. 2011 Zwaan et al. 2010 Slide 14 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. Slide 15 Fabello et al.
2012 HI mass fraction Based on HI stacking of ALFALFA data for GASS
galaxies. As M group (N) increases, the HI mass fraction decreases.
Evidence for ram pressure stripping in moderate density
environments. Slide 16 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 Slide 17 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 f gas, N detections and increase in HI distribution in
groups (with group mass) suggests ram pressure stripping is
occurring even in moderate density environments. Slide 18 Local vs.
Global Environment Isolated vs. Void galaxies Compact groups vs.
Loose Groups Different regions of Clusters Slide 19 Isolated
Galaxies Total HI Intensity Contours on Optical 1,5,10,50,100 x 10
19 cm -2. Pisano et al. 2003 UGC 11152 IC 5078 UGC 260 NGC 6368 29%
(12/41) of isolated galaxies have companions or signatures of
recent interaction/accretion. Slide 20 CIG 340 (Scott et al.
2014)CIG 292 (Portas et al. 2011) CIG 85 (Sengupta et al. 2012) CIG
96 (Espada et al. 2005) AMIGA Isolated Galaxies 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 asymmetric
compared to 10-20% of field galaxies (Espada et al. 2011) Slide 21
Problem with Profiles HI distributionHI profile It is impossible to
unambiguously find signatures of interactions, asymmetries, or a
companion with just an HI profile. Slide 22 Kreckel et al. 2011,
2012 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. Slide 23
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 N HI = 10 18 cm -2.
Filament has peak N HI = 2x10 18 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) Slide 24 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. Slide 25 Verdes-Montenegro et al. 2001 Compact Groups 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.
Slide 26 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). Slide 27 HI at the 10 17 cm -2 level in
the Local Group Thilker et al. 2004; Braun & Thilker 2004N HI =
0.5 20 x 10 18 cm -2 Slide 28 But is this really diffuse? 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 Slide 29 It is not associated with nearby
dwarf galaxies. The clouds are at different velocities than M31s
HVCs and its dwarf companions, so they are a different phenomenon.
Wolfe et al. 2013 Slide 30 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 Slide 31 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. Slide 32 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?
