1. ARCCOS Centre of Excellence in Evolutionary Cosmology Local Group Analogs: Where are the HVCs? Centre for Astrophysics & Supercomputing Swinburne University Brad Gibson D.J. Pisano, Ken Freeman, Lister Staveley-Smith, David Barnes, Virginia Kilborn Tim Connors, Daisuke Kawata

2. ARCCOS Centre of Excellence in Evolutionary Cosmology Motivation Observational Search for Intragroup Gas Clouds Computational Search for Anomalous Velocity Gas Clouds Conclusions Local Group Analogs: Where are the HVCs?

3. ARCCOS Centre of Excellence in Evolutionary Cosmology Motivation (the “higher” goals) Is galaxy assembly/formation still occurring today? Specifically, are HI clouds around galaxies and in galaxy groups associated with galaxy formation? What do these data say about models of galaxy formation in groups of galaxies? What do these data say about the evolution of galaxies in different environments?

4. ARCCOS Centre of Excellence in Evolutionary Cosmology Motivation (a different tack) High-Velocity Clouds The Satellite/Substructure Problem

5. ARCCOS Centre of Excellence in Evolutionary Cosmology Galactic HVCs: What? Where? How? kinematics inconsistent with Galactic rotation no stellar component unknown distances (Chris Thom) large sky covering factor origin scenarios: fountains, tidal debris, building blocks

6. ARCCOS Centre of Excellence in Evolutionary Cosmology Local Group HVCs? Blitz et al. (1999) suggested that most HVCs were associated with low-mass dark matter halos and had d  1 Mpc and M HI  10 7 M  Braun & Burton (1999) suggested that just the compact HVCs had these properties de Heij et al. (2002) proposed the CHVCs are concentrated around the Milky Way and M31 with a Gaussian distance distribution with D  150 - 200 kpc and M HI ≤ 10 7 M  All of these models associate HVCs with galaxy formation The latter models associate HVCs with dark matter halos

7. ARCCOS Centre of Excellence in Evolutionary Cosmology The Satellite/Substructure Problem Cold Dark Matter models of galaxy formation predict  300 dark matter halos in the Local Group, most with velocity widths less than 20 km/s, but only  20 satellites known. Is the Local Group typical? Could the remaining DM halos be associated with HVCs or are they devoid of baryons? Gill, Knebe & Gibson (2003)

8. ARCCOS Centre of Excellence in Evolutionary Cosmology Testing the Hypothesis If CHVCs are associated with the “missing satellite” dark matter halos and group/galaxy formation, then we should see them in other groups. If CHVCs are tidal debris, galactic ejecta, or something else, then they will not be so ubiquitous.

9. ARCCOS Centre of Excellence in Evolutionary Cosmology Since HVCs could be a group phenomenon, perhaps we should look for them in groups. We observed the entire area of 6 spiral-rich, loose groups with the Parkes Multibeam and ATCA. Our Local Group Analog Survey

10. ARCCOS Centre of Excellence in Evolutionary Cosmology What is a Loose Group? A working definition is: A grouping of a few large galaxies and tens of smaller ones, with the large galaxies typically separated by 100-200 kpc. They are of order 1 Mpc in total extent. The Local Group of galaxies is a loose group. Of particular interest are analogs to the Local Group which are dominated by spiral galaxies. We observed 6 such groups with Parkes and ATCA.

11. ARCCOS Centre of Excellence in Evolutionary Cosmology Groups observed: LGG 93, 106, 180, 293, 478, HIPASS Group 3 Composition: All spiral + irregular galaxies No X-ray emission. Group distances: 10.6 - 13.4 Mpc Number of galaxies in optically defined group: 3 - 9 Group velocity dispersions: 30 - 300 km/s Average diameter of groups: 1.6 Mpc Average galaxy-galaxy separation: 550 kpc Group Properties

12. ARCCOS Centre of Excellence in Evolutionary Cosmology Groups observed: LGG 93, 106, 180, 293, 478, HIPASS Group 3 Area observed: 1-2 Mpc 2 ≈ 25 - 35 sq. deg. Velocity Resolution: 1.65 or 3.3 km/s Velocity Coverage: 1700 - 3400 km/s Spatial Resolution: 14´ = 50 kpc Mass sensitivity (1   M HI over 3.3 km/s): 5 - 8 x 10 5 M  Parkes Multibeam Observations

13. ARCCOS Centre of Excellence in Evolutionary Cosmology The LGG 93 Group IC 1914

14. ARCCOS Centre of Excellence in Evolutionary Cosmology New Detections LGG 93

15. ARCCOS Centre of Excellence in Evolutionary Cosmology 110 HI-rich objects detected towards the 6 groups 67 HICAT sources in the same fields 64 HI-rich objects in the 6 groups 33 optically cataloged group galaxies Parkes Survey Results

16. ARCCOS Centre of Excellence in Evolutionary Cosmology ATCA Observations Purpose: Confirm detections, ID optical counterparts, find confused sources Number of sources: 110 potential galaxies Area observed: 30´ FOV = 100 kpc Velocity Resolution: 1.65 or 3.3 km/s (same as Parkes) Velocity Coverage: 1700 km/s centered on galaxy Spatial Resolution: 2´ ≈ 7 kpc Mass sensitivity (1   M HI over 3.3 km/s): 5 - 8 x 10 5 M  (Same as Parkes Observations!)

17. ARCCOS Centre of Excellence in Evolutionary Cosmology LGG 93 ATCA Followup

18. LGG 93-2 IC 1914 LGG 93-1 LSBG F200-023 AM 0311-492 No HI detections of any HVCs in ATCA data! ATCA Observations: LGG 93 Followup

19. Optical Counterparts All but one new source cataloged in NED. No HI clouds without stars found yet! M HI /L B = 6.3 M HI = 5 x 10 7 M  LSBG F200-023 M HI /L B = 5.6 M HI = 7 x 10 7 M  AM 0311- 492

20. ARCCOS Centre of Excellence in Evolutionary Cosmology Detected all known optically-cataloged group galaxies (33 galaxies). 64 HI detected galaxies in the 6 groups, 40% of which were not detected in HIPASS. All but 2 of 110 galaxies detected with Parkes are confirmed with ATCA. All detections have optical counterparts. HI masses are 10 7 -10 9 M . No HI clouds without stars found!!! Two Parkes sources found to be pairs of galaxies. ATCA Survey Results

21. If CHVCs are associated with the formation of the Local Group or the galaxies therein, then they should be in other groups. (Pisano et al. 2004, ApJ, 610, L17) A Simple CHVC Model As D HWHM decreases, we expect less detections. As the population decreases, we expect fewer detections. undetected detected

22. Expected Distances D HWHM = 50 - 500 kpc For D HWHM = 50 kpc, average CHVC M HI = 1.5 x 10 5 M . For D HWHM = 200 kpc, average CHVC M HI = 6 x 10 5 M . For D HWHM = 500 kpc, average CHVC M HI = 1 x 10 7 M . We do NOT detect average CHVC analogs, but only the most massive ones. If population of CHVC analogs is different, this model may not be valid.

23. D HWHM < 160 kpc Combined Constraints for 3 groups M HI < 4 x 10 5 M  Blitz et al. 99 BB99

24. ARCCOS Centre of Excellence in Evolutionary Cosmology Summary of Observations Non-detections imply HVCs must be within D HWHM < 160 kpc at 95.45%confidence level. Average CHVC M HI < 4 x 10 5 M  Total HI Mass in CHVCs < 1 x 10 8 M  Therefore, There is very little NEUTRAL gas around the Milky Way to participate in galaxy formation. Yet, it can still provide fuel for star formation. May be plenty of ionised gas! Furthermore, Unless M DM /M HI = 100, the total mass in CHVCs is much less than the total mass in the Milky Way or M31, and they are dynamically unimportant.

25. ARCCOS Centre of Excellence in Evolutionary Cosmology “This is a great piece of science. I pray that after this paper, the number of papers you get claiming to "disprove" the Blitz et al. model of HVCs will drop to zero. It's the best argument against it yet, and it distills all the other, weaker arguments.” - Bob Benjamin (referee) -

26. ARCCOS Centre of Excellence in Evolutionary Cosmology Multi-resolution Cosmological Disks with GCD+ M vir = 6x10 9 M  V max = 65 km/s J-band High-z snapshot High Resolution Region m DM =2x10 5 M , ε DM =0.14 kpc, m gas =3x10 4 M , ε gas =0.08 kpc Kawata & Gibson (2003a,b)

27. ARCCOS Centre of Excellence in Evolutionary Cosmology Dark Halo Anomalous Velocity Gas in Cosmological “Milky Way” Disk Simulations

28. ARCCOS Centre of Excellence in Evolutionary Cosmology fraction of sky covered by anomalous high-velocity gas comparable to Milky Way distribution of velocities also comparable to Milky Way by analogy with simulation, conclude that HVC gas is at d<150 kpc

29. ARCCOS Centre of Excellence in Evolutionary Cosmology Summary Observational  There are many detections of HI clouds around individual galaxies in nearby Local Group analogs, but none of these can be unambiguously associated with galaxy formation  no HI clouds without stars down to M HI < 5x10 6 M   Non-detections imply HVCs must be within 150 kpc at the 95% c.l. Very little neutral gas remaining for galaxy assembly, however there may be a significant reservoir of ionised gas.  original Blitz et al. (1999) and Braun & Burton (1999) models are ruled out

30. ARCCOS Centre of Excellence in Evolutionary Cosmology Summary Computational  Low density environment cosmological N-body + Hydrodynamical simulations of L * disk galaxies naturally yield anomalously high- velocity neutral hydrogen gas clouds with spatial and kinematical properties comparable to those of the Milky Way’s HVC population (Tim Connors’s thesis)  The galactocentric distances to these simulated HVCs is 10-50 kpc, with a tail out to <150 kpc (consistent with above observational program and direct distance constraints from Chris Thom’s thesis)  Under the assumption of collisional ionisation equilibrium (no doubt flawed), an associated population of ionised OVI anomalous velocity clouds are distributed over the range 30-400 kpc, but the sky covering fraction as a function of limiting OVI column density is  2 orders of magnitude lower than observed (resolution-related issues? Conduction fronts? Photoionisation?)

31. ARCCOS Centre of Excellence in Evolutionary Cosmology