Wide-Field HI Galaxy SurveysThe Arecibo Legacy Fast ALFA (ALFALFA)

Survey and its Predictions for Future Surveys

Martha HaynesCornell University

STScI13 June 2011

ALFA is not a car…

ALFA is not a car…

Arecibo L-band Feed Array (ALFA)

It is a radio “camera”

Arecibo L-band Feed Array (ALFA)

It is a radio “camera”

ALFA is not a car…

Arecibo L-band Feed Array (ALFA)

It is a radio “camera”

• 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

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

http://egg.astro.cornell.edu/alfalfa

ALFALFA, a Legacy Survey

http://egg.astro.cornell.edu/alfalfa

ALFALFA, a Legacy Survey

Check out the ALFALFA blog!

•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

•ALFA beams are 3.3’x3.8’

•“Almost” fixed azimuth drift mode

•2nd pass offset from the first to give 1.05’ samplingALFALFA survey strategy:

Keep it simple! “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’ samplingALFALFA survey strategy:

Keep it simple! “Minimum intrusion”99% open shutter time

The ALFALFA team: An open collaboration

Riccardo Giovanelli PI

Heavy student involvement:

• 6 PhDs to date• 11 PhDs underway• 125+ undergrads• Dozens of undergrad

thesis projects

Undergrad ALFALFA team

39 papers in refereed literature (appeared or submitted)

No full-time professional staff

1. Census of HI in the Local Universe over cosmologically significant volume

2. Determination of the faint end of the HI Mass Function and the abundance of low mass gas rich halos

3. Environmental variation in the HI Mass Function

4. Blind survey for HI tidal remnants

5. Determination of the HI Diameter Function

6. The low HI column density environment of galaxies

7. The nature of HVC’s around the MW (and beyond?)

8. HI absorbers and the link to Ly absorbers

9. OH Megamasers at intermediate redshift 0.16 < z < 0.25

ALFALFA Science Goals

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

ALFALFA 40% catalog

Lowest mass systems:•detected only nearby•narrow velocity widths

FAA radar

.40 sampleHaynes+2011

FAA harmonic +GPS/NUDET

Virgo

Haynes+ 2011 (about to be submitted)

Mining ALFALFASignal 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

Fabello+ 2011 MNRAS (in press)

ALFALFA pipeline tracks RFI/continuum => Spectral stacking

to dig deeper

Silvia Fabello PhD thesis

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

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”

4 tile centered at

+26

• 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: SDSSBlue: ALFALFA

Inner zone

Full bandpass

“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)

HI-selected galaxies

• 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…)

SED fitting (SDSS+GALEX)

Shan Huang PhD thesis

HIMF from ALFALFA: Good news for the SKA!

HIPASS: Zwaan+2005

.40: Martin+2010

N=10119

N=4315

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

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)

Ann MartinPhD 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

GALEX FUV

GMRT

Preliminary; Chengalur+

=> HI velocity field

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?

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 PapastergisPhD thesis

Baryon fractions as fn of halo mass

Simulations of different resolution;

lowest = filled circles;

highest = unfilled squares.

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?

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 = 5.44SHIELD: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

Hoeft+ 2006

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 CHVCsMHI ~ 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.

ALFALFA UltraCompact HVCs: LG Minihalos?

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

2.8x105 MM/L > 50

Ryan-Weber+

2007

Betsey AdamsPhD 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 easyHI 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

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

HI 21 cm emission ~ 106 X less power than Hα

GPS NUDET

2-d (freq vs time) “drift”

Future of Wide Area HI SurveysWALLABY (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 redshiftDetecting 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 studiese.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

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”

ASKAPMeerKAT

http://arecibo.tc.cornell.edu/hiarchivehttp://egg.astro.cornell.edu/alfalfa

ALFALFA sprouts!

•ALFA beams are 3.3’x3.8’

•“Almost” fixed azimuth drift mode

•2nd pass offset from the first to give 1.05’ samplingALFALFA survey strategy:

Keep it simple! “Minimum intrusion”99% open shutter time