‘‘The chase for Minihalos ‘The chase for Minihalos ‘ (or whatever the (or whatever the title I sent in was)title I sent in was)

or “From High Velocity Clouds or “From High Velocity Clouds to High Velocity Clouds, to High Velocity Clouds, by the way of TF”by the way of TF”

Riccardo GiovanelliRiccardo Giovanelli Cornell UniversityCornell University

Green Bank, April Green Bank, April 20122012

Credit: Virgo collaboration (MPIfAp)Credit: Virgo collaboration (MPIfAp)

Numerical simulations Numerical simulations predict the existence of predict the existence of lots of low mass halos:lots of low mass halos:

Do they exist in the Do they exist in the expected numbers?expected numbers?

•Are baryons blown away Are baryons blown away by the first generation of by the first generation of stars?stars?•Is gas accretion & Is gas accretion & cooling impeded by UV cooling impeded by UV heating in low M halos?heating in low M halos?•Are baryons retained Are baryons retained but unable to make but unable to make stars?stars?•Is that more likely in Is that more likely in cosmic voids?cosmic voids?

The Missing Satellite The Missing Satellite ProblemProblem

Klypin et al 1999Klypin et al 1999

Tikhonov & Klypin Tikhonov & Klypin (2009) claim (2009) claim observations fall short observations fall short by factor > 10by factor > 10

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 theCDM mass-concentration relation: CHVCs ARE TOO LARGE

-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

Simulations with Gastrophysics

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

Do we have any chance to ever observe these guys?109 Msun halo < 107 Msun baryons

Sternberg, McKee & Wolfire 2002Sternberg, McKee & Wolfire 2002

A plausible model A plausible model for a baryon-poor for a baryon-poor minihalo:minihalo:

kpcRMM

MM

MM

HI

sunHI

sunbaryon

sunhalo

7.0103

105

103

5

6

8

Mass of the Mass of the Warm, ionized Warm, ionized gas (WIM)gas (WIM) Virial Halo MassVirial Halo Mass

ALL PLOTSALL PLOTS

Contours of HI (WNM) radius (kpc) HI column density HI MassContours of HI (WNM) radius (kpc) HI column density HI Mass

ALFALFA can detect ALFALFA can detect this kind of beast out this kind of beast out to 2-3 Mpcto 2-3 Mpc

… … so let’s look nearbyso let’s look nearby

Substructure in the Local GroupSubstructure in the Local Group

Giant spiralsGiant spiralsdSph (+dEll)dSph (+dEll)dIrrdIrrdIrr/dSphdIrr/dSph

Gas-rich Gas-rich dwarfs live dwarfs live in the in the periphery periphery of the LGof the LG

Note

… … so let’s look nearby so let’s look nearby for something that for something that looks like:looks like:

• Angular diameter : < 10’

• Linewidths: 15-30 km/s• Peak flux: tens of mJykpcR

MM

MM

MM

HI

sunHI

sunbaryon

sunhalo

7.0103

105

103

5

6

8

cz=264 km/scz=264 km/sW50=24 km/sW50=24 km/sMMHIHI =3.1x10 =3.1x1055 D D22 M Msunsun

Credit: T. Osterloo, Spineto 2007

HI mass = 3x105 MsunHIMass/L_V = 5 M_dyn=8x106 Msun… and still forming stars… [80% of visible baryons in HI]

HVCs in footprint of ALFALFA, North Galactic CapHVCs in footprint of ALFALFA, North Galactic Cap = 1620 sq deg= 1620 sq deg

N=71 positive HVCs N=71 positive HVCs V VLSRLSR>130 km/s>130 km/sN=44 negative HVCs N=44 negative HVCs V VLSRLSR<-100 km/s<-100 km/s

LG galaxiesLG galaxies

HVCs in footprint of ALFALFA, North Galactic Cap = 1620 sq deg

LG galaxies within D=2.6 Mpc (away from center of LG)

V_LS

R [k

m/s

]

22 minihalo candidates

RG+ (2010) Distances are not knownNote: Leo T would not be detectable in either SDSS or DSS if d=1 Mpc

Betsey Adams preparing a broader catalog of minihalo candidates

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.

We have found a subset of the HVC phenomenon We have found a subset of the HVC phenomenon that appears to be compatible with the minihalo that appears to be compatible with the minihalo hypothesis.hypothesis.

Other interpretations are possible, we have not Other interpretations are possible, we have not proved that the candidates are LG minihalos, but proved that the candidates are LG minihalos, but that is a tantalizing possibility.that is a tantalizing possibility.

We need to detect similar features in nearby galaxy We need to detect similar features in nearby galaxy groups. That will require groups. That will require - significant increase in telescope survey speed - significant increase in telescope survey speed and/orand/or- deep optical images searching for optical - deep optical images searching for optical counterpartscounterparts

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

Looking for P1 analogs beyong the Looking for P1 analogs beyong the LGLG

• 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 feedCryogenically cooled, proposed by Cornell in 2007 and currently being prototyped by Cornell/BYU for use at AO

• With some luck, we could begin sucha survey in 2014.

19-beam PAF (Cornell/BYU) prototype for

“AO40”

To obtains a template TF relation, use a basket of clusters...

… + calibrators: over the volume sampled by the template:H_o = 69+/-6 (km/s)/Mpcaveraged over a volume ofcz = 9500 km/s radius(Giovanelli+ 1996).

…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 tocz ~ 20,000 km/s