1 / 20

‘The chase for Minihalos ‘ (or whatever the title I sent in was) or “From High Velocity Clouds

‘The chase for Minihalos ‘ (or whatever the title I sent in was) or “From High Velocity Clouds to High Velocity Clouds, by the way of TF”. Riccardo Giovanelli Cornell University Green Bank, April 2012. The Missing Satellite Problem.

ailani
Download Presentation

‘The chase for Minihalos ‘ (or whatever the title I sent in was) or “From High Velocity Clouds

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. ‘The chase for Minihalos ‘(or whatever the title I sent in was) or “From High Velocity Clouds to High Velocity Clouds, by the way of TF” Riccardo Giovanelli Cornell University Green Bank, April 2012

  2. The Missing Satellite Problem Numerical simulations predict the existence of lots of low mass halos: Do they exist in the expected numbers? Klypin et al 1999 Tikhonov & Klypin (2009) claim observations fall short by factor > 10 • Are baryons blown away by the first generation of stars? • Is gas accretion & cooling impeded by UV heating in low M halos? • Are baryons retained but unable to make stars? • Is that more likely in cosmic voids? Credit: Virgo collaboration (MPIfAp)

  3. HVCs: an Intergalactic Population? Blitz et al (1999):” HVCs are large clouds, with typical diameters of 25 kpc, containing 3x107 solar of neutral gas and 3x108 solar of dark matter, falling towards [the barycenter of] the Local Group; altogether the HVCs contain 1010 solar of neutral gas.” Braun & Burton (1999): The “undisturbed” minihalos appear as Compact HVCs, which have typical sizes of 0.5 deg and FWHM linewidts 20-40 km/s Problems: 1. If HVCs (or CHVCs) are bona fide LG members, they should also exist in galaxy groups other than the LG: NOT SEEN (see DJ) 2. Sternberg et al (2002) show that, in order to fit DM halo models to the CHVCs, their HI fluxes and angular sizes constrain them to be no farther than 150 kpc, else they famously violate the LCDM mass-concentration relation: CHVCs ARE TOO LARGE

  4. Simulations with Gastrophysics • Hoeft et al. (2006) simulated the SF processes in voids, using code that included radiative processes, SN feedback and an external, photoionizing Hardt & Madau (1996) UV background, with a resolution that allows monitoring evolution of DM halos of mass as low as 2.3x108 Msun. • Small halos DO NOT retain their share of baryons • Note dependence on simulation resolution Characteristic halo Mass Mc: that which retains 50% of its baryons

  5. Do we have any chance to ever observe these guys? 109 Msun halo  < 107 Msun baryons Sternberg, McKee & Wolfire (2002) have investigated the gastrophysics of minihalos: the remaining baryons in a low mass halo are capable of developing a small WARM NEUTRAL phase (WNM), possibly detectable through its HI emission. … ‘though HI mass only a fraction of baryon mass

  6. Contours of HI (WNM) radius (kpc) HI column density HI Mass Sternberg, McKee & Wolfire 2002 A plausible model for a baryon-poor minihalo: Mass of the Warm, ionized gas (WIM) ALL PLOTS Virial Halo Mass ALFALFA can detect this kind of beast out to 2-3 Mpc

  7. … so let’s look nearby

  8. Giant spiralsdSph (+dEll)dIrr dIrr/dSph Substructure in the Local Group Gas-rich dwarfs live in the periphery of the LG

  9. Note

  10. … so let’s look nearby for something that looks like: • Angular diameter : < 10’ • Linewidths: 15-30 km/s • Peak flux: tens of mJy

  11. cz=264 km/s W50=24 km/s MHI =3.1x105 D2Msun

  12. HI mass = 3x105 Msun HIMass/L_V = 5 M_dyn=8x106 Msun … and still forming stars… [80% of visible baryons in HI] Credit: T. Osterloo, Spineto 2007

  13. HVCs in footprint of ALFALFA, North Galactic Cap W = 1620 sq deg N=71 positive HVCs  VLSR>130 km/s N=44 negative HVCs  VLSR<-100 km/s LG galaxies

  14. HVCs in footprint of ALFALFA, North Galactic Cap W = 1620 sq deg LG galaxies within D=2.6 Mpc (away from center of LG) V_LSR [km/s]

  15. 22 minihalo candidates RG+ (2010) Distances are not known Note: Leo T would not be detectable in either SDSS or DSS if d=1 Mpc Betsey Adams preparing a broader catalog of minihalo candidates

  16. ALFALFA Minihalo Candidates at D=1 Mpc • Mean HI Mass 3x105 solar • Mean HI Diameter 0.7 kpc • Mean avged HI column density 1019.1 cm-2 • Mean avged HI density 0.006 cm-3 • Mean total mass within RHI 3x107 solar • Sternberg et al (2002) Minihalo Template @ P=10 cm-3 K • HI Mass 3x105 solar • HI Diameter 0.7 kpc • Peak HI column density 1019.6 cm-2 • WIM Mass 6x106 solar • Total mass within Rvir 3x108 solar At the distance of nearby groups of galaxies, the ALFALFA minihalo candidates would have been below the sensitivity limit of extant HI surveys.

  17. We have found a subset of the HVC phenomenon that appears to be compatible with the minihalo hypothesis. Other interpretations are possible, we have not proved that the candidates are LG minihalos, but that is a tantalizing possibility. We need to detect similar features in nearby galaxy groups. That will require - significant increase in telescope survey speed and/or - deep optical images searching for optical counterparts

  18. WIYN image, credit: J. Salzer & K. Rhode

  19. Looking for P1 analogs beyong the LG • In the absence of a stellar component, it is impossible to determine distances to HI minihalo candidates in the LG • Solution: look in nearby groups (D ~3-5 Mpc) for which redshift can imply group membership ( “a’ la DJ”) • Need: coverage of several 100 sqd and 10X ALFALFA sensitivity • “AO40” – 40 beam phased array feed • Cryogenically cooled, proposed by • Cornell in 2007 and currently being • prototyped by Cornell/BYU for use at • AO • With some luck, we could begin such • a survey in 2014. 19-beam PAF (Cornell/BYU) prototype for “AO40”

  20. To obtains a template TF relation, use a basket of clusters... …and confirm the kinematic nature of the Dipole of the Peculiar Velocity Field … and convergence to the CMB dipole is confirmed by the LG motion w.r.t. a set of 79 clusters out to cz ~ 20,000 km/s … + calibrators: over the volume sampled by the template: H_o = 69+/-6 (km/s)/Mpc averaged over a volume of cz = 9500 km/s radius (Giovanelli+ 1996).

More Related