Slide 1

Galaxy Luminosity Function (LF) (yes, another use of phee!) - What are the relative numbers of galaxies of different luminosities?N = (L) L VN is the # of galaxies that are located in volume V with luminosities between L and L+L(L) has units # galaxies/(luminosity interval x volume)

Can also be written in terms of absolute magnitude N = (M) dM where N is total number of galaxies per unit volume-Field Galaxy LF measure apparent brightness of galaxies in some sample (i.e. field)convert apparent to absolute magnitude from estimated distanceapply k-correction if distance is more than 400 Mpc.divide # of galaxies in each magnitude/luminosity interval by volume of space surveyednote that V is greater for intrinsically brighter galaxies in a survey with fixed apparent magnitude limitProblems: Malmquist Bias in magnitude limited surveysDistance estimate uncertainties enhancements (clusters/walls) and voids in galaxy distribution (for a given magnitude, N can depend on spatial distribution as much as )

Field LF reveals 1) # density of galaxies declines w/increasing L2) decline increases sharply at some characteristic luminosity L*

Schechter (1976) found LF well described by

(L) = */L* (L/L*) exp(-L/L*)this is the SLF* = 5.5 x 10-3 galaxies/Mpc3L* = 2 x 1010 LsunM*B = -20.4 = -1.070.07(Efstathiou, Ellis, & Peterson 1988)Move to K-band (IR) to avoid domination of light by star forming regions and sample more typical stars

(Gardner at al. 1997)* = 5.5 x 10-3 galaxies/Mpc3L* = 2 x 1010 LsunM*K = -23.8 = -0.9 0.22MASS (Kochanek et al. 2001)* = 4.1 x 10-3 galaxies/Mpc3L* = 2 x 1010 LsunM*K = -23.4 = -1.09 0.06 Even though different wavelengths are dominated by different stellar types, LFs are virtually the same in optical and infrared.In optical bands (from SDSS: Montero-Dorta & Prada 2008)

Remarks about SLFworks for all galaxies lumped together; individual galaxy types not as well fitMilky Way and Andromeda are close to or just fainter than L*galaxies with L 3L* are very rareSLF predicts too many galaxies at low L (as L 0, N )Calculate total # of galaxies in some volume whose luminosity exceeds L

N(>L) = (L) dL = * x e-x dx = * (1+) (recall (z) = tz-1 e-t dt)

for -1, as L 0, N(>L) Thus, SLF fails at low L with -1 L=L x=L/L*Calculate total luminosity of galaxies

Ltot = (L) L dL = * L* x+1 e-x dx

Ltot = * L* (2+) * L* with = -1

So, Ltot is finite for = -1 even though Ntot goes to infinity... phew! x=0 0Cluster Galaxy LFeasier to obtain since all galaxies are at the same distance and together in the skydifficult since rich clusters are rare and typically at greater distances

Cluster LFs are reasonably well fit with SLF and thus are similar to the field.Main differences: is steeper ( -1.3)* is larger due to increased density in clusters compared to fieldexcess of bright galaxies (e.g. cD galaxies do not fit well into SLF)

LF divided by Morphological Type

-early and late type galaxies separate in LF-somewhat similar but note differences

From Las Campanas Redshift Survey with SLF fit to all galaxies

M*R = -21.1 = -0.7 0.05

LF divided by Morphological Type

-early and late type galaxies separate in LF-somewhat similar but note differences(from SDSS: Montero-Dorta & Prada 2008)

Jerjen & Tammann (1997) decomposed LF into morphological classes (B-band values)Spirals Gaussian shape with = -17.6, = 1.4 magS0s Gaussian shape with = -18.3, = 1.1 magEs Gaussian skewed to bright end with = -17.7Irr SLF with M* = -15.8, = -0.3dE SLF with M* = -16.7, = -1.3High L cut-off occurs at same place for field and clusters because of characteristic M* for Sps and Es and their similarity

Steeper slope for clusters comes from increased population of dEs

Galaxy GroupsMore poorly clustered and containing fewer members than clustersContain mostly disk systems spirals and Irre.g. Ursa Major group of brightest 79 galaxies, only 2 are EsRandom velocities of galaxies are slower than cluster members = 700 1200 km/s for cluster galaxies = 100 500 km/s for group galaxies

Thus, group galaxies affect each other more than do cluster galaxies gravity has time to pull at gas and stars

Stephans Quintet rare compact group109 Msun hot gas (Tx~107K)1010 Msun cool gasgas primarily intergalactic (galaxies are mostly stripped of gas)gas heated to high temperatures due to collisionsThe Local Group

about 35 40 galaxies within ~1.5 Mpc of MWbrightest member Andromeda (M31)other spirals MW and M33No bright ellipticalsMore than half are dEs and dSphsRest are irregulars (Magellanic Clouds)Probably missing some objects near the galactic planee.g. Sagittarius dwarf just discovered in 1994 (Ibata, Gilmore & Irwin 1995)More than 90% of Local Group galaxies have Mv fainter than -18 (3 x 109 Lsun)

Milky Way, Andromeda and M33 emit 90% of visible light from the Local Group!

Sb, Sbc, ScIrr/dIrrdSphdEMW & Andromeda moving toward each other at 120 km/s

Galaxy Collisions and MergersIn groups, galaxy collisions and mergers can be important

Galaxy with mass M moves with velocity V past star of mass m in another galaxyM/m ~ 108 - 1011Galaxy M acquires motion perpendicular to path

Applies if galaxy M is small enough that its core radius rc