ALFALFA:

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ALFALFA
The Arecibo Legacy Fast ALFA Extragalactic HI
Survey (The Search for Low-Mass, Gas-Rich Halos)
Martha Haynes (Cornell University) for the
ALFALFA team
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ALFA is not a car
It is a radio camera
Arecibo L-band Feed Array
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..on Arecibo 305m telescope
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ALFALFA as a Legacy Survey

• One of several major surveys currently ongoing at
  Arecibo, exploiting its new multibeam capability

• An extragalactic spectral line survey
• Covers 7000 sq deg of high galactic latitude sky
• 1345-1435 MHz (-2000 to 17500 km/s for HI line)
• 5 km/s resolution
• 2-pass, drift mode (total int. time per beam
  40 sec)
• 1.5-2 mJy rms
• 4000 hrs of telescope time, 6-7 years
• started Feb 2005 as of end of 2006, 1/3 complete

http//egg.astro.cornell.edu/alfalfa
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The Void Phenomenon
Peebles (2000)

• Cosmic voids are filled with low mass dark matter
  haloes

vrotgt55km/s

• 1000 haloes with M lt 109M? and vrotlt 20 km/s in
  a 20 h-1 Mpc void are predicted

Halo mass function in voids Gottlöber et al
(2003)
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Luminosity function of void galaxies

• Void LF has a faint M but a similar faint-end
  slope, compared to the overall LF
• Void galaxies are blue, disk-like and have high
  H? equivalent width

Void galaxies in the SDSS Hoyle et al (2005)
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The Missing Satellite Problem

• Models/simulations predict large numbers of
  satellites
• Kauffmann et al. (1993)
• Klypin et al. (1999)
• The current census does not count them.
• Faint end slope of the optical LF
• Faint end slope of the HIMF
• Willman et al. (2005) suggest that more than half
  of the MW satellites have not been identified
  because of extinction, surface brightness limits

• Nothing to detect?
• Baryon loss during reionization ( e.g.,
  Efstathiou 1992 Barkana Loeb 1999 Shaviv
  Dekel 2003)
• Can they (ever) form stars? (Verde et al. 2002)

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Dwarf galaxies
Leo A

• dE, dSph, dIrr
• Low mass detected only nearby
• Dark matter dominated
• Low abundances
• Stellar mass 106-108 M?
• Blue Luminosity 106-108 L? (MBgt -15)
• Dynamical mass 107-109 M?
• Where they are gas-rich
• HI mass 106-108 M?
• Sometimes, extensive HI
• Evidence for dark matter

Carina
Sagittarius
IZw18
LGS3
SBS0335-052
Dwarf galaxies of the Local Group Mateo 1998
ARAA
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Substructure in the Local Group

• Galaxies mainly clustered around the two
  principal galaxies MW M31
• Morphological segregation evident
• dE/dSph near large galaxies
• dI at larger distances

Diagram from Grebel 1999
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The Search for Low Mass Halos

• Do large numbers of low mass halos exist?
• If so, do they contain baryons?
• If so, could they be starless but gas-rich?
• gt Extragalactic HI survey
• If so, could they be found preferentially in some
  environments but not in others?
• gt Fair sample

ALFALFA is designed to detect low mass gas-rich
halos
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The HI Mass Function

• Previous surveys have included few (if any)
  objects with HI masses less than 108 M?.
• At lowest masses, differ by 10X
• Rosenberg Schneider (2000)
• versus
• Zwaan et al. (1997)

?
Parkes HIPASS survey Zwaan et al. 2003
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Environment the HIMF

• Previous studies based only on Virgo have
  suggested that the HIMF in Virgo is shallower
  than in the field
• Only a single cluster
• Very small number statistics
• Is this just HI deficiency?
• Watch out for morphological biases
• Springob, Haynes Giovanelli (2005)
• Much larger sample, but optically targeted
• Used PSCz density field out to 6000 km/s
• Low mass end of HIMF in high density regions
  flatter and M lower
• Cannot be explained simply by morphology or HI
  deficiency.
• Zwaan et al. (2005) HIPASS seems inconsistent
• ALFALFA will provide needed statistics and be HI
  blind.

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Previous surveys for HI in voids

• for example
• Weinberg et al 1991 (PPS foreground void)
• Szoromu et al 1994
• Szomoru et al 1993 (HI in Bootes void galaxy)
• Szomoru et al 1996a (Bootes void)
• Szomoru et al 1996b
• Pustilnik et al 2002 (Blue compact galaxies)

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HI in famous voids

• VLA surveys
• Szomoru et al (1996) Bootes void

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HI in famous voids

• VLA surveys
• Szomoru et al (1996) Bootes void

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HI in famous voids

• VLA surveys
• Szomoru et al (1994) PPS foreground void

Void PPS
fields 30 12
Int. time/field 40 min 210 min
rms/beam 1 mJy 0.4 mJy
detections 0 17

• Serious limitations
• Relatively small volume sampled
• Bandwidth only 6.25 MHz (1200 km/s)
• Velocity resolution 42 km/s (too wide)

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ALFALFA Survey

• Commensal with TOGS HI
• Does not compete with galactic plane surveys

High galactic latitude sky visible from AO
Supergalactic plane
Virgo
Leo
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ALFALFA Science Goals

1. Determination of the faint end of the HI Mass
   Function and the abundance of low mass gas rich
   halos
2. Environmental variation in the HI Mass Function
3. Blind survey for HI tidal remnants
4. Determination of the HI Diameter Function
5. The low HI column density environment of galaxies
6. The nature of HVCs around the MW (and beyond?)
7. HI absorbers and the link to Ly ? absorbers
8. OH Megamasers at intermediate redshift 0.16 lt z lt
   0.25

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ALFALFA as a Blind HI Survey

• HI mass and distribution (for extended objects)
• Normal, star-forming disks
• Potential for future star formation (HI content)
• HI deficiency in clusters
• History of tidal events
• Low mass, LSB dwarfs
• HI absorption optical depth
• Link to Ly-a absorbers
• Redshifts
• Rotational velocities
• Dark matter
• Distances via Tully-Fisher relation

HI in M31
Credit R. Braun
? SdV HI mass V Distance ?V
Mass
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ALFALFA as a Blind HI Survey

• HI mass and distribution (for extended objects)
• Normal, star-forming disks
• Potential for future star formation (HI content)
• HI deficiency in clusters
• History of tidal events
• Low mass, LSB dwarfs
• HI absorption optical depth
• Link to Ly-a absorbers
• Redshifts
• Rotational velocities
• Dark matter
• Distances via Tully-Fisher relation

Credit A. Chung
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ALFALFA as a Blind HI Survey
Durrell DeCesar Yun 1994

• HI mass and distribution (large objects)
• Normal, star-forming disks
• Potential for future star formation (HI content)
• HI deficiency in clusters
• History of tidal events
• Low mass, LSB dwarfs
• HI absorption optical depth
• Link to Ly-a absorbers
• Redshifts
• Rotational velocities
• Dark matter
• Distances via Tully-Fisher relation

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ALFALFA as a Blind HI Survey

• HI mass and distribution (large objects)
• Normal, star-forming disks
• Potential for future star formation (HI content)
• HI deficiency in clusters
• History of tidal events
• Low mass, LSB dwarfs
• HI absorption optical depth
• Link to Ly-a absorbers
• Redshifts
• Rotational velocities
• Dark matter
• Distances via Tully-Fisher relation

I Zw 18 van Zee et al. 1998
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Are there totally dark galaxies?
Arecibo map outer extent Hoffman et al. 1993
DDO154
MH 2.5 x 108 M? Mstars 5.0 x 107 M?
MDyn 3.0 x 109 M?
Extent of Optical image
Carignan Beaulieu 1989 VLA D HI
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HI 122501
Optical galaxy
M L
gt 200
Giovanelli, Williams Haynes 1989
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The ALFALFA Team

• ALFALFA is a collaboration of gt50 people, from
  34 institutions in 13 countries.
• ALFALFA is an open collaboration anybody with a
  valid scientific interest and a hardworking
  disposition can join.

• Legacy survey on a national telescope used not
  only for radio astronomy but also radar studies
  of Solar System objects and the Earths upper
  atmosphere
• Heavy student involvement
• Broad institutional representation

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Participating Institutions

• Cornell University
• NAIC
• NRAO
• Lafayette College
• Union College
• Wesleyan University
• Harvard/Smithsonian CfA
• U. of Michigan
• Indiana U.
• Rutgers U.
• U. of Minnesota
• U. of Wisconsin
• St. Lawrence U.
• Humboldt St. U.
• Colgate U.
• Georgia Southern U.
• NRL
• NASA/GSFC

• U. of Crete
• U. of Tel-Aviv
• U. of Rome
• U. of Milan II
• Obs. Of Brera
• U. of Provence
• Arcetri Astrophys. Obs.
• Lab. DAstrophysique/Marseille
• Cardiff U.
• U. de Barcelona
• U. de Cordoba (Argentina)
• NCRA/GMRT (India)
• P. U. Cat. de Chile
• Special Astrophys. Obs. (Russia)
• U. of Kiev

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ALFALFA a wide area survey
To sample more deeply, you have to integrate A
LOT longer!
Beam dilution
Giovanelli et al. 2005, AJ130, 2598

For low masses larger solid angle
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ALFALFA strategy Keep it simple!
ALFA beams are 3.3x3.8 Almost fixed azimuth
drift mode 2nd pass offset from the first to give
1.05 sampling
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Automated signal detection

• Signal extraction in the Fourier domain by Amélie
  Saintonge

• Match filter over a range of widths of the
  template
• e.g. 10 km/s 600km/s
• Choose the width for which the convolution is
  maximized --gt position of the signal
• Calculate the amplitude of the signal from the
  width

• Run on 3-D datacubes after completion of tile
• Once signals identified, further interactive
  analysis

Slide Amelie Saintonge
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Exploit VO tools during data processing

• Data processing tools developed here at CU are
  now running at 11 other institutions
• VO tools incorporated to allow access to external
  datasets during data processing
• DSS, DSS2, Sloan, 2MASS, NVSS images can be
  fetched
• NED and other on-line catalogs, including our
  own, can be accessed and overplotted.

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VO portal

• ALFALFA data products will be made public as
  soon as possible.
• Targeted HI survey and precursor data already
  available
• Remember we need a complete dataset both
  passes to make a grid.
• Issue is serving data volume/local cpu
• google ALFALFA

http//arecibo.tc.cornell.edu/hiarchive
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Current Status (by 15 Dec 2006)
Total blocks 177 145
Total hours 1070 690
In map region 1010 625
07h30 16h30 04 to 16 deg 22h00 03h00
12 to 16 deg 24 to
32 deg

• 1/3 of survey covered with 2 passes (by 15Jan07)
• Processing requires complete sky coverage
• Riccardo will present only 4 of final survey

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Comparison of blind HI surveys
Survey Beam Area rms
min MHI Ndet ts Nlos
arcmin sq. deg. (mJy _at_
18 km/s) _at_ 10 Mpc sec
AHISS 3.3 13 0.7
2.0x106 65 var 17,000 ADBS
3.3 430 3.3 9.6x106
265 12 500,000 HIPASS
15. 30,000 13 3.6x107
4315 460 1.9x106 HIJASS 12.
(TBD) 13 3.6x107 (?)
3500 (TBD) J-Virgo 12 32
4 1.1x107 31 3500
3200 HIDEEP 15 32 3.2
8.8x106 129 9000 2000 ALFALFA
3.5 7,000 1.7 4.4x106
20,000 30 7x106
ALFALFA will be 1 order of magnitude more
sensitive than HIPASS with 4X better angular
resolution, 3X better spectral resolution, and
1.6X total spectral bandwidth
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ALFALFA Precursor

• Giovanelli et al 2005 AstronJ 130, 2598 2613
• Aug-Sep 2004
• Candidate Detections Confirmation Run Jan-Feb
  2005
• 36 hours of ALFA data

166 confirmed HI sources - 25 with HI mass gt
1010 M? - 4 with HI mass lt 107 M? (twice as
many as all of HIPASS) - high positional
accuracy gt optical counterparts IDd -
slightly better detection rate than expected
(high side), i.e. our ability to
reliably dig in low S/N territory is high -
system hardware performance, hands-off bandpass
calibration and baselining (IDL
processing pipeline) yield
EXCELLENT data quality
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Precursor (ALFA commissioning phase) results
HIPASS Completeness Limit
HIPASS Detection Limit
HIPASS would have detected only a handful and
none of the low mass ones.
F
Integrated Flux of 1 Jy km/s
In 36 hours, we detected 4X more lowest mass
objects than all of HIPASS
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First ALFALFA catalog
Giovanelli et al (2006, Astron. J.
submitted) Northern Virgo cluster region 11h44m lt
R.A. lt 14h00m 12º lt DecJ lt 16º 716 detections
of good/excellent quality Median redshift 7000
km/s In the same sky region, HIPASS detected
only 40 objects. HIJASS Virgo survey region of
maximum sensitivity ALFALFA 193
detections HIJASS 13
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ALFALFA Hunting in/around voids

• ALFALFA is designed to hunt for low mass systems
  efficiently
• High sensitivity (Arecibo 1/10th SKA!)
• Efficient 97 open shutter time
• Large solid angle (7000 sq deg)
• Moderate angular resolution (3.5) gt optical
  i.d. - or none!
• High spectral resolution (5 km/s)
• Minimum intrusion gt high data quality
• Dual pol/2 pass coverage (confirmation)
• Automated signal detection

• HI mass function to low masses, and its
  environmental dependence
• HI detections HST distances gt shapes and
  kinematics of voids
• Tikhonov Karachentsev 2006 astro-ph/0609109
• Evolutionary history of isolated (never
  interacting!) galaxies

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Riccardo will talk next, after tea