DLA Surveys and Stats Sandhya Rao University of Pittsburgh

Outline  A bit of history  DLAs at high redshift (z>1.65)  HI stats at z = 0  DLAs at low z  New results at low z  MgII, FeII, N(HI) correlations  dn/dz, Ω, f(N)  Star formation history of DLAs a paradigm shift

The First DLA: Title: Absorption Lines in the Quasistellar Object PHL 957. Authors: Lowrance, J. L., Morton, D. C., Zucchino, P., Oke, J. B., & Schmidt, M. Bibliographic Code: 1971BAAS L Lowrance et al. 1972, ApJ, 171, 233 Beaver et al. 1972, ApJ, 178, 95 Hale telescope Image-tube 5Å resolution Lick Observatory Image-tube 8Å resolution

Black, Chaffee, & Foltz 1987, ApJ, 317, 442 MMT spectrograph CCD 1Å resolution

Optical surveys for DLAs:  The Lick Survey for DLAs Wolfe, Turnshek, Smith, & Cohen first systematic search for DLA candidates - z ≈ 2 - follow-up spectroscopy to confirm detections Turnshek et al. 1989, Wolfe et al DLAs in 68 spectra, Δz=55  Lanzetta et al expanded sample, 1.6<z< DLAs in 156 spectra, Δz=155 - first determinations of dn/dz, Ω, f(N) vs. z  Wolfe et al LBQS: 62 DLAs in 228 spectra, Δz=324 - SF model to explain Ω, f(N) Motivation: Milky Way column densities Low ions & narrow fwhm’s Low 21 cm spin temps  search for high z disks

Optical surveys for DLAs (contd):  Storrie-Lombardi & Wolfe extended survey to z=4.7 using LRIS on Keck - 85 DLAs along 646 sightlines, Δz=420  Peroux et al. 2001, surveyed 66 QSOs at z> additional DLAs, 15 at z>3.5 - LLS include half the Ω at z>3.5  Prochaska & Herbert-Fort used SDSS-DR1 spectra, 71 DLAs in 1252 QSOs - a total of 163 DLAs in high-z statistical sample - most sensitive at z=2 — LLS contribute <15%

HI at the present epoch  Need a statistical description of HI at z=0 to help interpret DLA stats.  The relevant questions are: 1.How much of it is there?  Ω 2.What is its cross-section?  dn/dz 3.What is the column density distribution?  f(N) 4.Where does it reside, and have we found it all?

 Rao and Briggs 1993 (pre- HI, pre-large-galaxy surveys era) - used the optical luminosity function of gas-rich galaxies + HI maps of a ‘complete’ sample of 27 nearby galaxies f(N) ~ ∫ Φ(M) dM ∫ f(N)dN ~ dn/dz ∫ Nf(N)dN ~ Ω

 Rao and Briggs 1993 (pre- HI, pre-large-galaxy surveys era) - used the optical luminosity function of gas-rich galaxies + HI maps of a ‘complete’ sample of 27 nearby galaxies f(N) ~ ∫ Φ(M) dM ∫ f(N)dN ~ dn/dz ∫ Nf(N)dN ~ Ω

 Rao and Briggs 1993 (pre- HI, pre-large-galaxy surveys era) f(N) ~ ∫ Φ(M) dM ∫ f(N)dN ~ dn/dz ∫ Nf(N)dN ~ Ω

 HI 21cm surveys: HI Mass Function and f(N) distribution  AHISS: Arecibo HI Strip Survey — Zwaan et al  HI survey of the Ursa Major cluster — Zwaan, Verheijen, & Briggs 1999  ADBS: Arecibo Dual Beam Survey — Rosenberg & Schneider 2001  HIPASS: HI Parkes All Sky Survey — Zwaan et al. 2003, Zwaan et al Ryan-Weber et al  HIDEEP: 20x deeper in 4° x 8° fld — Minchin et al. 2003, 2004

 HI 21cm surveys: HI Mass Function and f(N) distribution Current status of results:  All gas rich galaxies are included in the optical luminosity function. (Until last month, that is.)  Ω HI (z=0) is still dominated by massive, HI rich galaxies (spirals), but LSB contribution is now 30%. Larger than RB93 result by 40%.  dn/dz is larger than RB93 result by about a factor of 3.  The contribution of LSB galaxies to the HI cross-section, 40%, is larger than previously thought.

Thanks to large surveys, DLA stats at high z and HI stats at z=0 are much better understood now than they were a few years ago. There is no all-sky UV spectroscopic survey of QSOs (one can only wish!), but we managed to get the best out of STIS before its untimely demise.

The need for UV surveys

DLAs at low redshift: UV surveys IUE Survey: Lanzetta, Wolfe, & Turnshek 1995 HST Key Project: Jannuzi et al IUE+HST Archival Survey: Rao, Turnshek, & Briggs 1995 HST-FOS Survey: Rao & Turnshek 2000 HST-STIS Survey: Rao, Turnshek, & Nestor 2005

Our approach : High-z DLAs have MgII, SiII, CII, FeII absorption MgII ( 2796Å, 2803Å) can be seen in the optical at z > 0.1 We targeted QSOs that had low-z MgII absorption MgII statistics (dn/dz and REW distribution) are known  bootstrap from MgII stats to DLA stats

 Rao & Turnshek (2000): MgII systems from literature ( primarily Steidel & Sargent 1992) HST-FOS Cycle 6 survey + HST Archival survey: 12 DLAs in 81 MgII systems with W > 0.3Å + 4 more in a Cycle 9 survey  Rao, Turnshek, & Nestor (2005): MgII Systems from SDSS EDR (Dan Nestor 2004, PhD Thesis, U. Pittsburgh) 118 HST orbits – 1 of 7 Large Programs approved in Cycle SDSS QSOs with 82 MgII systems ≤ z ≤ Å ≤ W ≤ are DLAs The MgII-DLA Surveys  We now have a sample of 197 MgII systems at z < 1.65 that have measurements of N(HI). 41 are DLAs.

MgII REW distribution Shaded histogram: DLAs

MgII 2796 REW vs. log HI column density of all 197 systems. Solid circles: DLAs

Fraction of systems that are DLAs increases with W. But the mean value of N(HI) remains constant for W>0.6. = (3.4±0.7)E20 cm -2 There are no DLAs for W = (9.7±2.7)E18 cm -2.

Fraction of systems that are DLAs increases with W. And the mean value of DLA N(HI) decreases for W>0.6.

Fraction of systems that are DLAs increases with W. But the mean value of N(HI) remains constant for W>0.6. = (3.4±0.7)E20 cm -2 There are no DLAs for W = (9.7±2.7)E18 cm -2. W = 0.6 Å implies a spread in sightline velocity of Δv = 64 km/s. DLAs do not have kinematic spreads less than this. Turnshek (tomorrow): kinematic spread metallicity halo mass, galaxy type

MgII-FeII selection  W ≥ 0.3 Å : 21% DLAs  W ≥ 0.6 Å : 27% DLAs  W ≥ 0.5 Å + W ≥ 0.5 Å : 36% DLAs Red: all systems slope = 1.12 ± 0.06 Blue: DLAs only slope = 1.30 ± 0.11

All DLAs remain if the sample is restricted to W / W < 2. 38% DLAs

MgII 2796 vs. MgI  2852 W / W < 2. The DLAs occupy a regime where Å. 43% DLAs Upper limits not plotted.

Number of DLAs per unit redshift n DLA (z) = dn/dz High z: Prochaska & Herbert-Fort 2004 Low z: Rao, Turnshek, & Nestor 2005 z=0: Ryan-Weber et al. (2005) Zwaan et al. (2005)

No-evolution curve in the “737” cosmology. h=0.7 Ω M =0.3 Ω Λ =0.7

n(z) = n 0 (1+z)    = 1.2 No-evolution curve and power-law fit.

Cosmological Neutral Gas Mass Density in DLAs: Ω DLA (z) Ω lum (z=0) SDSS LF Panter et al Ω g (z=0) HIPASS Zwaan et al. 2005

Out with the old, in with the new. Much better.

Ω DLA is constant for 0.5 < z < 4.5. Ω DLA = (9.7 ± 0.1) x Ω gas (z=0) = (4.88 ± 0.56) x 10 -4

The HI column density distribution function f(N) Low z slope = -1.4 ± 0.2 High z slope = -1.8 ± 0.1 z=0 slopes: -1.4 ± 0.2, log N(HI) < ± 0.9, log N(HI) > 20.9

Now, all three results together: Simple picture: High z: higher comoving c.s./volume, lower Low z: lower comoving c.s./volume, higher constant mass density Column densities increase as clouds condense and mergers proceed, and then decrease when star formation depletes gas?

The Star Formation History of Galaxies Compilation of SFR measurements by A. Hopkins (2004) + parameterization: Hopkins, Rao, &Turnshek 2005 (submitted)

The Star Formation History of DLAs global Schmidt Law – Kennicutt 1998  * = n DLA Σ SFR = 4.0 x n DLA Σ gas dX/dz. 1.4 Σ gas = m H dX/dz = (c/H 0 )(1+z) 2 /E(z) E(z)=(Ω M (1+z) 3 + Ω Λ ) 0.5 Hopkins, Rao, & Turnshek 2005 (in units of Msun/yr/Mpc 3 )

Evolution of the mass density in metals.    63.7  Z Conti et al Calura & Matteucci 2004 ◦ Dunne et al (submillimeter) ● Rao, Prochaska, Wolfe, Howk 2005 Mass density in metals derived from the SFR history...

 (baryon) Fukugita & Peebles 2004  (DLA) evolution of stellar mass density derived from SFRs.  (gas) assuming that the total gas+stellar mass density at all epochs equals the z=0 value of  (DLA)+  (stars). Stellar mass density and DLA gas mass density

DLAs do not trace the majority of the neutral gas at all epochs - particularly at high redshifts. 1.This can’t be attributed to missed QSOs due to dust obscuration: Ellison et al. radio loud QSOs DLA survey. 2.Contribution from subDLAs? Peroux et al. claim 50% of neutral gas mass at z>3.5 could be from subDLAs; but refuted by Prochaska & Herbert-Fort. 3.Explains disparity in  (metals). Low average metallicity + low gas mass density = metal mass density much lower than in luminous galaxies. 4. Very likely that very high column density systems have very low gas cross-sections, and are missed in QSOAL surveys. Evidence for this is shown in the next few slides.

Global Schmidt Law from Kennicutt M sun /pc 2 = 1.2 x cm -2

Incidence of SFR surface densities from Lanzetta et al From high-z DLA f(N) distribution From galaxies in the HDFs At high redshift: DLAs and luminous galaxies are distinct populations. Column densities up to 4 orders higher are observed in the luminous population. If the highest SFR density objects have gas radii 2 orders smaller than DLAs, they will contribute to dn/dz and Ω. Integral SFR density in DLAs is higher than integral SFR density in luminous objects! Luminous galaxy surveys do not include DLAs. DLA surveys do not include luminous galaxies. However, at low z there is some overlap.

 (baryon) Fukugita & Peebles 2004  (DLA) evolution of stellar mass density derived from SFRs.  (gas) assuming that the total gas+stellar mass density at all epochs equals the z=0 value of  (DLA)+  (stars). Stellar mass density and DLA gas mass density starsgas

Summary 1. 43% of MgII systems with 1 Å <W2796/W2600 < 2 Å and MgI W2852 > 0.2 Å are DLAs. And DLAs are confined to these regimes. 2.dn/dz evolves from high redshift to z=1.5 or 2 and then does not. 3. Ω DLA stays flat from z≈5 to z≈0.5. DLA value of Ω is 2x larger than z=0 value. 4.f(N) changes with redshift: seems to show assembly of high density clouds at z>2 followed by depletion due to star formation. 5.By comparing star formation histories of luminous galaxies and the gas in DLAs, one has to conclude that DLAs do not trace all the neutral gas, particularly at high z, and luminous galaxies do not trace all the star formation at high z.

DLA galaxy properties

Water Erosion Water erosion erodes little things like sand into the water. That can sometimes be a problem.