ALFALFA: Preliminary Results

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ALFALFA Preliminary Results from a strip
through Virgo
Catalog in preparation Brian Kent et al.
RA 0900h to 1400h Dec 12deg to 16deg Solid
Angle 291 sq deg (4 of survey)
Catalog in preparation Sabrina Stierwalt et al.
R. Giovanelli Cornell University
Catalog in preparation R. Koopmann et al.
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?
Sources of log (HIMass)lt7.5 N12
N42
Parkes HIPASS survey Zwaan et al. 2003
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Problem with Virgo/foreground Distances
RA Range 1144 1400 (largely Virgo)
0900 - 1400
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HIPASS Completeness



HIPASS Limit
A Comparison with HIPASS
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A Comparison with HIPASS, HIJASS, etc

• Over the 132 sq. deg. including the northern part
  of Virgo, i.e. RA1144-1400, Dec14.-16.0
• ALFALFA detects 716 sources, HIPASS 40 (2
  unconfirmed)
• While this region is perhaps the most intensively
  studied
• in the local Universe, at all wavelength bands
  (including
• HI, using optically selected samples),
• ? 69 of ALFALFA detections are new (the
  conventional
• wisdom on which optical targets would turn
  out to be
• HI-rich appears to have been limited)
• Over the region of max HIJASS sensitivity
• ? ALFALFA detects 193 sources, HIJASS 15

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czlt5000

• HI (ALFALFA)
• N1709

5000ltczlt10000
10000ltczlt18000
czlt5000
czlt18000
5000ltczlt10000
Optical ? N2529
10000ltczlt18000
czlt18000
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• HI (ALFALFA)
• N1709

Optical ? N2529
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Centroiding HI 20 (med)
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So what do we find?
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800 pc
Distance 8 Mpc
HPBW3.8x3.3
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A high z LSB log(HI Mass)9.86
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A low z LSB log(HI Mass)8.89
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A nearby LSB log(HI Mass)7.75
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A few goodies in Virgo
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Two stray clouds
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Brian Kent et al. (in preparation)
4.76 x 107 M?
7.29 x 107 M?
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1o300 kpc
IC3068 BCD cz1288
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1o300 kpc
IC 679 Sbc cz2213
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The Cardiff Dark Galaxy
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NGC 4254
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DSS2 Blue
45 kpc
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Combined ALFALFA data around NGC 4254
cz 2243 to 2557 km/s
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45 kpc
Haynes et al. (in preparation)
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Combined ALFALFA data around VIRGOHI21
cz 1946 to 2259 km/s
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45 kpc
Haynes et al. (in preparation)
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220 kpc
Minchin et al 2005 (WSRT)
Haynes et al. (in preparation)
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Haynes et al. (in preparation)
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A cloud complex
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MHI 0.83E8 solar V 527 km/s W 120 km/s
MHI 0.52E8 solar V 601 km/s W 45 km/s
MHI 1.9E8 solar V 605 km/s W 257 km/s
235 kpc
MHI 1.7E8 solar V 490 km/s W 66 km/s
MHI 0.75E8 solar V 476 km/s W 48 km/s
100 km/s 100 kpc/Gyr
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VCC1357 0.2x0.1 I? 603 km/s
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NGC4424 3.6x1.8 SBa 476 km/s
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• Cloud complex is in Virgo cluster
• Complex is not gravitationally bound
• Cloud-to-cloud Dv 100 km/s, Dr 100 kpc
• ? mean cloud separation will double in 1 Gyr
• ? cloud complex is transient phenomenon,
• at first pass through the cluster
• If individual clouds are bound their individual
• total masses average 1-2 x 10 9 solar

• Possible Origin
• Group of mini-halos falling in cluster for first
  time
• Separated outskirts from single spiral galaxy
• Satellites separated from main galaxy in group

HYDRO (Ram Pressure)? TIDAL (gravi)?
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Galaxy harassment?
High velocity, - but long-lasting - encounters in
a cluster can drastically impact galaxy evolution.
Animation by G. Lake
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A Void Dweller
Most of the mass within the HI boundaries is
accounted by the HI itself
cz3264 km/s MHI 3.5x108 Msun
GMRT Map
Amelie Saintonge et al. (2007, in prep)
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Does metallicity correlate with local density?
galaxies in voids Popescu et al (1999) /
Hidalgo-Gamez et al (1998)
? Amelie Saintonge, Ph.D. Thesis, Cornell 2007
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Extremely metal-poor galaxy
cz 280 km/s W 27 km/s F 0.64 Jy km/s D 6.3
Mpc log(MHI) 6.77
DSS2B
Alfalfa Spectrum
HI014127, a metal-poor galaxy Saintonge et al.
(in prep)
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Extremely metal-poor galaxy
Most of the mass within the HI boundaries is
accounted by the HI itself
Ha
WISE (N.Brosch)
WIYN0.9m
log(O/H)12 7.4
Radius 400 pc
HI014127, a metal-poor galaxy Saintonge et al.
(in prep)
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And then there are lots of narrow features, near
the noise, with no optical counterpart theyll
be chased one by one
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some more credible than others
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• The LSS characteristics of HI-selected galaxies
  are the same as those optically-selected, albeit
  with lower density contrast
• ALFALFA does not detect a population of high mass
  (say gt 1010 solar), optically inert systems
  (e.g. Cardiff dark galaxy)
• A number of optically inert systems are detected,
  which appear to be of tidal origin
• ALFALFA detects a numerically conspicuous pop of
  HI-rich, optically faint, low mass systems
  dynamics within the boundaries of the HI appear
  dominated by the HI mass
• Candidate sources w/o optical counterparts are
  either of apparent tidal origin or have very
  narrow (lt30 km/s) linewidths will need
  corroboration
• A population of HVCs with positive velocities
  (czgt150 km/s) near the NGP may be related to
  nearby, low mass galaxies

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Were just getting started. Stay tuned