Statistical Properties of Radio Galaxies in the local

Universe

Yen-Ting LinPrinceton University

Pontificia Universidad Católica de ChileYue Shen, Michael Strauss, Ragnhild Lunnan (Princeton), Zheng Zheng (IAS)

outline

• motivations• science goals

– consensus of radio galaxies (RGs) hosted by massive galaxies in the local universe (z0.3)

– formation mechanism of RGs– identification of interesting objects for detailed study

• the sample• several statistics to look at

– relationship with radio-quiet (RQ) population– dependence on the environment

motivation: to make the bright end of the luminosity function

right

Croton et al (2006)

motivation: SZ surveys are happening!

credit: CXO

Carlstrom et al (2002)

Atacama Cosmology Telescope in construction

see Lin et al (0805.1750) for estimation of effects of radio sources on SZ signal

• using NYU-VAGC DR6 LSS galaxy sample as parent sample, containing ~220,000 galaxies down to Mr–20.5 (about M*)

• cross-matched with NVSS and FIRST surveys at 1.4 GHz to generate the largest radio galaxy catalog to date: 10,500 RGs stronger than 3mJy

• improvements over previous studies– construction of several volume-limited subsamples– 90% of RGs have measured redshift– all RGs visually inspected to secure matches and measurement

of fluxes– morphology information of radio sources– high S/N measurement of correlation functions– halo occupation distribution (HOD) modeling

the sample

bivariate luminosity function

whole sample M-20.5 volume-limited M-21.5 volume-limited

optical luminosity function

• 0.02z0.132• 108,873 galaxies• 2,253 RGs• 2.1% of galaxies

more luminous than M* have radio power logP23.12

• fiber collision correction applied

correlation function

• both galaxies and RGs are volume-limited and subject to same optical luminosity cut (Mr–21.5)

• RGs (red) more strongly clustered than galaxies (blue)

• clustering length comparable to groups of galaxies (~10h-1Mpc)

correlation function: HOD modeling

• consider NRG=NRG,cen+NRG,sat

• NRG,cen=1 if(MMmin)• NRG,sat=(M/M1)

• HOD modeling suggests RGs are hosted by halos more massive than 1013 Msun (consistent with lensing results from Mandelbaum et al 2008)

RGs in massive halos: halo occupation number

• count galaxies and RGs at Mr–20.5 in 134 X-ray clusters from ROSAT all-sky survey

• number of galaxies goes as M0.8

• occupation number of RGs not a strong function of cluster mass

• 1435 galaxies, 85 RGs (~6%)• 62/134 (=46%) clusters host

RGs• among these, 34 have RL BCGs• 44 clusters host only 1 RG, 20 of

these are BCG• 25% of BCGs are RL• 3.9% of non-BCG galaxies are

RL• NOTE: 2.1% of galaxies are RL

globally BCGs

clusters w/o RGs

RGs in massive halos: spatial distribution

RGs in dense regions

• excess number of neighbors– 1000 RGs, 1000 RQ

galaxies matched to optical luminosity, apparent magnitude, and redshift

– count nearby objects out to 2 Mpc from SDSS photometric catalog, within –23.5Mr–20.5

– within ~0.5 Mpc, RL galaxies always have higher number of neighbors than RQ ones

Mpc

RGs in dense regions

no RLAGN–SF galaxy pairs atscales<1Mpc!

caution: small number ofSF galaxies in the sample!

summary

• observations:– given optical luminosity and color, RGs are more strongly clustered

than the corresponding RQ galaxy sample

– large scale clustering implies hosts are group or cluster-sized halos

– RGs very centrally concentrated towards halo center

• ingredients for RL AGN phenomenon– dense environment

– presence of intracluster/intragroup gas: confining pressure

– low level supply of gas: what’s the source?

• work in progress– dissection of the bivariate LF

– environment of high and low-excitation RL AGNs (e.g., FRI vs FRII)

– relationship with X-ray and optical AGNs