1. Wide-Field HI Galaxy Surveys
The Arecibo Legacy Fast ALFA (ALFALFA) Survey and its Predictions for Future Surveys
Martha Haynes
Cornell University
STScI
13 June 2011

2. ALFA is not a car…

3. Arecibo L-band Feed Array (ALFA)
ALFA is not a car…
It is a radio “camera”
Arecibo L-band Feed Array (ALFA)

4. Arecibo L-band Feed Array (ALFA)
It is a radio “camera”
Arecibo L-band Feed Array (ALFA)

5. Arecibo L-band Feed Array (ALFA)
ALFA is not a car…
It is a radio “camera”
Arecibo L-band Feed Array (ALFA)

6. ALFALFA, a Legacy Survey
One of several major surveys currently ongoing at Arecibo, exploiting its multibeam capability
An extragalactic spectral line survey
To cover 7000 sq deg of high galactic latitude sky
MHz (-2000 to km/s for HI line)
5 km/s resolution
2-pass, drift mode (total int. time per beam ~ 40 sec)
~2.3 mJy rms (at 10 km/s resolution)
=> MHI~105 M in LG, ~107 at Virgo
4400 hrs of telescope time, 5+ years (actual completion fall 2012)
Highly efficient: 99% “open shutter” time
Oversees acquisition of TOGS (galactic HI) data
Started Feb‘05; as of Apr’11, 92% complete (741 observing runs)
=> ALFALFA 40% catalog: detections covering a cosmologically significant volume at z=0

7. ALFALFA, a Legacy Survey
Check out the ALFALFA blog!

8. ALFA beams are 3.3’x3.8’
“Almost” fixed azimuth drift mode
2nd pass offset from the first to give 1.05’ sampling
“Minimum intrusion”
99% open shutter time

9. ALFA beams are 3.3’x3.8’
“Almost” fixed azimuth drift mode
2nd pass offset from the first to give 1.05’ sampling

10. ALFA beams are 3.3’x3.8’
“Almost” fixed azimuth drift mode
2nd pass offset from the first to give 1.05’ sampling
“Minimum intrusion”
99% open shutter time

11. ALFALFA survey strategy: Keep it simple!
ALFA beams are 3.3’x3.8’
“Almost” fixed azimuth drift mode
2nd pass offset from the first to give 1.05’ sampling
ALFALFA survey strategy: Keep it simple!
“Minimum intrusion”
99% open shutter time

12. ALFALFA survey strategy: Keep it simple!
ALFA beams are 3.3’x3.8’
“Almost” fixed azimuth drift mode
2nd pass offset from the first to give 1.05’ sampling
ALFALFA survey strategy: Keep it simple!
“Minimum intrusion”
99% open shutter time

13. The ALFALFA team: An open collaboration
Undergrad ALFALFA team
Riccardo Giovanelli PI
Heavy student involvement:
6 PhDs to date
11 PhDs underway
125+ undergrads
Dozens of undergrad thesis projects
39 papers in refereed literature (appeared or submitted)
No full-time professional staff

14. ALFALFA Science Goals
Census of HI in the Local Universe over cosmologically significant volume
Determination of the faint end of the HI Mass Function and the abundance of low mass gas rich halos
Environmental variation in the HI Mass Function
Blind survey for HI tidal remnants
Determination of the HI Diameter Function
The low HI column density environment of galaxies
The nature of HVC’s around the MW (and beyond?)
HI absorbers and the link to Ly  absorbers
OH Megamasers at intermediate redshift 0.16 < z < 0.25

15. ALFALFA 40% catalog .40 sample Haynes+2011 HIPASS completeness limit
HIPASS detection limit
HIPASS bandwidth edge
ALFALFA covers adequate volume with adequate sensitivity
detections
70% are “new”
Important advantages:
In addition to sensitivity, bandwidth and velocity resolution, ALFALFA yields positions to < 20”
Identify most probable optical counterpart (OC)
Continuum/RFI tracked
Allows stacking at arbitrary positions
FAA radar
FAA harmonic +
GPS/NUDET
Lowest mass systems:
detected only nearby
narrow velocity widths
.40 sample
Haynes+2011
Virgo
Haynes (about to be submitted)

16. Mining ALFALFA
Signal extraction done in Fourier domain using matched filter algorithm (Saintonge 2007, AJ, 133, 2087 )
HI flux density sensitivity depends on emission width => but well-behaved
Amélie Saintonge
PhD thesis
Gridview (Brian Kent)
Sources found by the signal extractor are examined interactively.
“Weight” at each 3-d grid point accounts for “missing” data (RFI)
Polarization match checked (RFI)
Continuum map retained
Optical field

17. Multiwavelength applications
Centroiding to <18”> (depends on S/N)
Optical images (SDSS, DSS2B) and databases (NED, AGC) examined along with HI field
Most probable OC
SDSS Photo/SpectObjIDs
“Priors” (lower S/N; same cz)
Extensive notes
Fabello MNRAS (in press)
ALFALFA pipeline tracks RFI/continuum
=> Spectral stacking to dig deeper
Silvia Fabello PhD thesis

18. Identifying Optical Counterparts
ALFALFA source centroids good to ~18” (depends on S/N)
ALFALFA catalogs include:
the HI centroid position
the position of the most probable OC
OC’s SDSS PhotoObjID and SpecObjID (where applicable)
Of sources in α.40:
1013 have no OC
844 of those could be HVCs (or LG minihalos)
199 (<2%) extragalactic
Of those, <50 are “isolated”

19. Red: SDSS Blue: ALFALFA 4 tile centered at +26 Full bandpass
7000 sqd of high galactic latitude sky with median cz ~8800 km/s
Undersamples clusters but traces well the lower density regions
Large overlapping areas with SDSS and GALEX
Red: SDSS
Blue: ALFALFA
Inner zone
4 tile centered at +26

20. “Dark” object in a group
ALFALFA HI on SDSS r
HI peak with no/marginal optical UV: almost dark?
MH, RG (CU), John Cannon (Macalester), John Salzer (Indiana)

21. SED fitting (SDSS+GALEX)
HI-selected galaxies
SED fitting (SDSS+GALEX)
Shan Huang
PhD thesis
Gas-dominated systems fill the blue cloud; but some gas-rich massive red spirals
GALEX-Arecibo-SDSS Survey (GASS: Catinella+ 2010; Schiminovich+2010) and COLDGASS (IRAM30m: Saintonge+2011a,b) => scaling relations for massive galaxies (ALFALFA detects about 30% of GASS targets)
High gas fraction massive HI disks: HIghMASS (colored symbols: stay tuned…)

22. HIMF from ALFALFA: Good news for the SKA!
Martin ApJ 723, 1359
Based on contiguous regions in Virgo vs anti-Virgo directions (35% of total)
10,119 Code 1 (“best”); cz < 15,000 km/s
ΩHI = 4.3 ± 0.3 x 10-4 (16% higher than HIPASS)
.40: Martin+2010
HIPASS: Zwaan+ 2005
Did not sample low/high mass ends
Issues of confusion in 15.5’ beam
Error bars are large!
Survey design must overcome cosmic variance and instrumental/selection bias
ALFALFA is the first blind HI survey to cover adequate volume at both the low and high HI mass ends
N=10119
HIPASS: Zwaan+2005
N=4315
Ann Martin
PhD thesis

23. HIghMass: High HI mass, gas-rich galaxies at z~0
ALFALFA detects a rich population with log MHI > 10.
Candidates to migrate from BC to RS but not yet reached phase of significant SF?
Alternative mode of (late) accretion?
=> higher than average spin parameter?

24. HIghMass: High HI mass, gas-rich galaxies at z~0
ALFALFA detects a rich population with log MHI > 10.
Candidates to migrate from BC to RS but not yet reached phase of significant SF?
Alternative mode of (late) accretion?
=> higher than average spin parameter?
GALEX FUV
GMRT
=> HI velocity field
Preliminary; Chengalur+
Shan Huang (PhD: GALEX, H, SED-fitting)
Betsey Adams (PhD: GMRT/WSRT)
Greg Hallenbeck (PhD:EVLA)

25. Where are the dwarfs? Papastergis+ ApJ (in press) astro-ph/1106.0710
ALFALFA Velocity Width Function (WF)
(to 20 km/s)
Are the low mass DM halos just “missing baryons”?
“Bolshoi”
Manolis Papastergis
PhD thesis

26. Baryon fractions as fn of halo mass
Hoeft et al 2006: Can small halos retain any baryons?
Ricotti (2009): Can gas accretion be reactivated at late z?
Leo T has 2.8x105 M of HI => prototype
Can we observe the threshold of baryon dropoff?
Simulations of different resolution;
lowest = filled circles;
highest = unfilled squares.

27. Low HI mass dwarfs: on the brink of extinction?
FIGGS (Begum +): <log MHI> ~ 7.78
Little THINGS (Hunter +): <log MHI> ~ 7.97
Leo T: log MHI = 5.44
Hoeft+ 2006
SHIELD:
EVLA BCD => 180 hours
John Cannon (PI); Betsey Adams (grad)
12 galaxies with <log MHI> ~ 6.7
Resolve HI => SF?
Trace DM halo

28. ALFALFA UltraCompact HVCs: LG Minihalos?
Leo T as nearby prototype: outside MW virial radius (dist~420 kpc)
We have found a subset of the HVC phenomenon that appears to be compatible with the LG minihalo hypothesis (Giovanelli+ 2010, ApJL 708,L22)
**much** smaller than the Blitz et al. and Braun&Burton CHVCs
MHI ~ 3 x 105 M; size ~ 0.7 kpc
Do not violate astrophysical constraints (Sternberg+ 2002)
Other interpretations are possible; we have not proved that the candidates are LG minihalos, but that remains a tantalizing possibility.
2.8x105 M
M/L > 50
On-going work (Betsey Adams, RG, MH, J.Salzer)
Optimize signal extraction algorithm => ALFALFA CHVC catalog
HI mapping: HI distribution, dynamics
Distances:
TRGB (resolved CMDs)
H: ionized by galactic RF places lower limit
Ryan-Weber+ 2007
Betsey Adams
PhD thesis

29. ALFALFA: Volume + Sensitivity
ALFALFA is the first blind HI survey to sample a cosmologically significant volume at z=0
Robust determination of HIMF at z=0
Work on ζ(r), VF and environmental variations on-going
There are no “dark” HI galaxies with HI masses > 109 M
ALFALFA sources provide the means to determine the baryon fraction as fn. of halo mass and test models of dropoff at Mhalo ~ 109 M
ALFALFA identifies a set of gas-rich Local Group “minihalo” candidates; evidence which will refute or confirm that hypothesis is being sought.
ALFALFA detects a previously-unrecognized population of very high HI mass galaxies with HI masses > 1010 M; in some, cool gas contributes the dominant form of baryons. => Good news for SKA!
There is more ALFALFA to be harvested!

30. Future of Wide Area HI Surveys
HI surveys are much less mature than OIR surveys
But understanding the gas is important!
HI selected samples very different from OIR selected surveys => star forming galaxies!
Wish list:
Deep survey of nearby grounds (sev hundred sqd) for Leo Ts
Wide area survey (~SDSS volume) with <10” angular resolution
Deep surveys at higher cz
Low column density diffuse HI surveys
(BAO/Intensity mapping; HERA experiments)
Technology advances will enable all this...

31. HI emission: simple but not easy
HI 21 cm line: τ ~ 10 Myr (3 x 1014 sec)
1 Mʘ = 2 x 1014 g => 1.2 x 1014 atoms of HI
Total HI gas (“normal”) = log [7-10]
HI emission ~ 4 x 1049 to 4 x 1052 photons per sec
L(HI 21 cm) ~ 4 x 1033 to 4 x 1036 ergs s-1
For comparison, in SF galaxies:
L(Hα) ~ 3 x 1039 to 3 x 1042 ergs s-1
HI 21 cm emission ~ 106 X less power than Hα
RFI from satellites:
Antenna arrays less affected if frontend not saturated
But no protected regions
Arrays (antenna arrays, phased array feeds) present huge challenges:
Required computations/datasets
Electrical power requirements
GPS NUDET
2-d (freq vs time) “drift”

32. Future of Wide Area HI Surveys
WALLABY (ASKAP) + WNSHS (APERTIF/WSRT)
Uncooled 37-beam PAF
Full sky survey out to z = 0.26
Resolution of 30” (maybe 10”) => where the gas is!
0.7 mJy/beam (per 50 km/s channel)
500,000 galaxies
e.g. WALLABY: 9600 hours (1200 points X 8hr)
A hunt for low mass halos (LeoTs) with AO40:
Cooled 40-beam PAF
10X ALFALFA sensitivity: 0.3 mJy/beam (per 5 km/s channel)
300 sqd over nearest groups (CVn, NGC 628/672/784)
1000+ hours
Diffuse HI (log NHI=17) survey with (clean beam) GBT
Limits on column density of gas (on 9’ scale)
See Jay Lockman’s poster

33. HI at higher redshift Detecting HI emission is really tough
Single galaxy at z = (Zwaan+ 2001; WSRT 200 hrs)
Single galaxy at z = (Verheijen+ 2004; VLA 80 hrs)
Two clusters at z=0.188 and (Verheijen+ 2007;WSRT 420 hrs)
42 galaxies detected with log MH: [ ]
26 (of 33) with z= [0.17 to 0.25] (Catinella+ 2008; Arecibo 300 hrs)
SKA pathfinders will make first foray into statistical studies
e.g. LADUMA on MeerKAT: (Baker/Blyth/Holwerda PIs)
5000 hours on EXDFS
Stacking at (pos,z) of known galaxies (few individual galaxies detected)
But… real progress awaits full SKA sensitivity

34. 19-beam PAF (NAIC/BYU) prototype for “AO40”
HI surveys: summary
HI emission line surveys are hard! But they yield important clues about cosmology and galaxy evolution (star forming galaxies!).
ALFALFA is the first blind HI survey that samples a cosmologically significant volume with the required sensitivity, solid angle and velocity resolution
Robust measures of HIMF, ΩHI, ξHI, VFHI at z=0
But it is limited in angular resolution (4’) and z
New array technologies (PAFs, antenna arrays) are enabling new capabilities => Lots to happen in the future!
19-beam PAF (NAIC/BYU) prototype for “AO40”
ASKAP
MeerKAT

35. ALFALFA sprouts! http://arecibo.tc.cornell.edu/hiarchive

37. ALFALFA survey strategy: Keep it simple!
ALFA beams are 3.3’x3.8’
“Almost” fixed azimuth drift mode
2nd pass offset from the first to give 1.05’ sampling
ALFALFA survey strategy: Keep it simple!
“Minimum intrusion”
99% open shutter time