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Wide-Field HI Galaxy Surveys

Wide-Field HI Galaxy Surveys. The A recibo L egacy F ast ALFA (ALFALFA) Survey and its Predictions for Future Surveys. Martha Haynes Cornell University. STScI 13 June 2011. ALFA is not a car…. ALFA is not a car…. It is a radio “camera”. Arecibo L-band Feed Array (ALFA).

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Wide-Field HI Galaxy Surveys

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  1. Wide-Field HI Galaxy Surveys TheArecibo 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. ALFA is not a car… It is a radio “camera” Arecibo L-band Feed Array (ALFA)

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

  5. 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 • 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

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

  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. 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. 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 • 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)

  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+ 2011 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 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”

  19. 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

  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. 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+ 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

  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 2010-2011 => 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 masshalos (LeoTs) with AO40: • Cooled 40-beam PAF • 10X ALFALFA sensitivity: 0.3 mJy/beam (per 5km/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 = 0.176 (Zwaan+ 2001; WSRT 200hrs) • Single galaxy at z = 0.189 (Verheijen+ 2004; VLA 80hrs) • Two clusters at z=0.188 and 0.206 (Verheijen+ 2007;WSRT 420hrs) • 42 galaxies detected with log MH: [9.7-10.6] • 26 (of 33) with z= [0.17 to 0.25] (Catinella+ 2008; Arecibo 300hrs) • 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. 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 http://egg.astro.cornell.edu/alfalfa

  36. 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

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