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

ALFA is not a car…

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

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

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

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 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) ~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: 15000+ detections covering a cosmologically significant volume at z=0 http://egg.astro.cornell.edu/alfalfa

ALFALFA, a Legacy Survey Check out the ALFALFA blog! http://egg.astro.cornell.edu/alfalfa

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

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

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

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

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

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

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

ALFALFA 40% catalog .40 sample Haynes+2011 HIPASS completeness limit HIPASS detection limit HIPASS bandwidth edge ALFALFA covers adequate volume with adequate sensitivity 15000+ 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+ 2011 (about to be submitted)

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

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+ 2011 MNRAS (in press) ALFALFA pipeline tracks RFI/continuum => Spectral stacking to dig deeper Silvia Fabello PhD thesis

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 15855 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”

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

“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)

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…)

HIMF from ALFALFA: Good news for the SKA! Martin+ 2010 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

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?

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)

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

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.

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 2010-2011 => 180 hours John Cannon (PI); Betsey Adams (grad) 12 galaxies with <log MHI> ~ 6.7 Resolve HI => SF? Trace DM halo

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

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!

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...

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”

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

HI at higher redshift Detecting HI emission is really tough Single galaxy at z = 0.176 (Zwaan+ 2001; WSRT 200 hrs) Single galaxy at z = 0.189 (Verheijen+ 2004; VLA 80 hrs) Two clusters at z=0.188 and 0.206 (Verheijen+ 2007;WSRT 420 hrs) 42 galaxies detected with log MH: [9.7-10.6] 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

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

ALFALFA sprouts! http://arecibo.tc.cornell.edu/hiarchive http://egg.astro.cornell.edu/alfalfa

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