1 / 38

ALFALFA:

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. ALFA is not a car…. It is a radio “camera”. Arecibo L-band Feed Array. ..on Arecibo 305m telescope.

sienna
Télécharger la présentation

ALFALFA:

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 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

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

  3. ..on Arecibo 305m telescope

  4. 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

  5. The Void Phenomenon Peebles (2000) • Cosmic voids are filled with low mass dark matter haloes vrot>55km/s • ~1000 haloes with M < 109Mand vrot< 20 km/s in a 20 h-1 Mpc void are predicted Halo mass function in voids : Gottlöber et al (2003)

  6. 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)

  7. 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)

  8. 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 (MB> -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

  9. Substructure in the Local Group Giant spiralsdSph (+dEll)dIrr dIrr/dSph • 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

  10. 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? • => Extragalactic HI survey • If so, could they be found preferentially in some environments but not in others? • => “Fair sample” ALFALFA is designed to detect low mass gas-rich halos

  11. 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

  12. 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.

  13. 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)

  14. HI in “famous” voids • VLA surveys: • Szomoru et al (1996): Bootes void

  15. HI in “famous” voids • VLA surveys: • Szomoru et al (1996): Bootes void

  16. HI in “famous” voids • VLA surveys: • Szomoru et al (1994): PPS & foreground void • Serious limitations: • Relatively small volume sampled • Bandwidth only 6.25 MHz (1200 km/s) • Velocity resolution ~42 km/s (too wide)

  17. ALFALFA Survey High galactic latitude sky visible from AO • Commensal with TOGS HI • Does not compete with galactic plane surveys Supergalactic plane Virgo Leo

  18. ALFALFA Science Goals • 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

  19. 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-α absorbers • Redshifts • Rotational velocities • Dark matter • Distances via Tully-Fisher relation HI in M31 Credit: R. Braun ∫ SdV HI mass V Distance ∆V Mass

  20. 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-α absorbers • Redshifts • Rotational velocities • Dark matter • Distances via Tully-Fisher relation Credit: A. Chung

  21. 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-α absorbers • Redshifts • Rotational velocities • Dark matter • Distances via Tully-Fisher relation

  22. 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-α absorbers • Redshifts • Rotational velocities • Dark matter • Distances via Tully-Fisher relation I Zw 18 van Zee et al. 1998

  23. 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

  24. HI 1225+01 Optical galaxy M L > 200 Giovanelli, Williams & Haynes 1989

  25. The ALFALFA Team • ALFALFA is a collaboration of >50 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 Earth’s upper atmosphere • Heavy student involvement • Broad institutional representation

  26. 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. D’Astrophysique/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

  27. 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

  28. ALFALFA 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

  29. Automated signal detection • Signal extraction in the Fourier domain byAmélie Saintonge • Match filter over arange of widthsof the template • e.g. 10 km/s – 600km/s • Choose the width for which the convolution is maximized-->positionof the signal • Calculate theamplitudeof the signal from the width • Run on 3-D datacubes after completion of “tile” • Once signals identified, further interactive analysis Slide: Amelie Saintonge

  30. 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.

  31. 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

  32. Current Status (by 15 Dec 2006) 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…

  33. Comparison of blind HI surveys Survey Beam Area rms min MHI Ndet ts Nlos arcmin sq. deg. (mJy @ 18 km/s) @ 10 Mpc sec AHISS 3.3 13 0.7 2.0x106 65 var 17,000 ADBS 3.3 430 3.3 9.6x106 265 12500,000 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

  34. 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 > 1010 M - 4 with HI mass < 107 M(twice as many as all of HIPASS) - high positional accuracy => optical counterparts ID’d - 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

  35. 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

  36. First ALFALFA catalog • Giovanelli et al (2006, Astron. J. submitted) • Northern Virgo cluster region • 11h44m < R.A. < 14h00m • +12º < DecJ < +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

  37. 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’) => optical i.d. - or none! • High spectral resolution (5 km/s) • “Minimum intrusion” => 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 => shapes and kinematics of voids • Tikhonov & Karachentsev 2006 astro-ph/0609109 • Evolutionary history of isolated (never interacting!) galaxies

  38. Riccardo will talk next, after tea

More Related