A comparison of the galaxy populations inthe coma and distant clusters

(Poggianti et al. 2004, ApJ, 601, 197)

orWhat it is like to teach Intro Astronomy

labs at ASU

Natalie R. HinkelJournal Club

1 February, 2007

Slide Count: 16

Jclub - 1 Feb, 08 1

Go Over the Syllabus

• Background• Observations• A bit of clarification• Comparing to the old galaxies• Looking at the faint galaxies• Previous work on Coma• Overview and conclusions

Jclub - 1 Feb, 08 2

Overview of What We Do

• Galaxies evolveusually via internalprocesses (SF) - butthe environment playsa part– No direction

correlation betweengalaxy morphologyand SF properties

– SF is suppressed frominfall/accretion

• Clusters present arange of physicalconditions to testevolution(s)

• Look at galacticspectra to figure outthe history

• Quantitativelycompare to a nearbycluster (z ~ 0.5) tobetter understandgalactic evolution

Jclub - 1 Feb, 08 3

Kill Them withNumbers

• Two 32.5 x 50.8 arcmin2 fields in the center(Coma1 - NGC 4874 and 4889) and SWcorner (Coma3 - NGC 4839)

• Spectra taken using the William HerschelTelescope at 5100ű1500Å, res 6-9 Å FWHM

• Targets selected from R-band mag-limitedsample with 4000 < v(km/s) < 10,000 andcutoff R ! 19– 189 galaxies in Coma1 and 89 in Coma3– 147 “dwarf” and 113 “giant” galaxies

Jclub - 1 Feb, 08 4

Pick-up the Pieces

• Properties indicated viaH! and emission (OII)– If no emission line and

EW(H!) > 3Å " k+a/a+kpoststarburst/forming, novigorous SF in last 1.5Gyr

– At least 1 emission line "emission-line spectrumongoing SF or AGN

– If no emission line andEW(H!) < 3Å " k spectrumpassive galaxy with no SFduring last 1.5Gyr

• aka E+A spectrum:spectra of anelliptical plus A-star

• K-spectrum: weakhydrogen lines, mostlyneutral metals (MnI,FeI, SiI), dominant inolder galaxies

• A-spectrum: stronghydgrogen lines,ionized metals (FeII,MgII, SiII, ~CaII)

Jclub - 1 Feb, 08 5

Lots of “Non-Science”Comparisons (MORPHS)

• Largest sample of clusters z > 0.3• Spectroscopic catalog containing 10 rich

clusters at z = 0.4-0.5 (Dressler et al. 1999),allows a direct comparison to new data

• Simple mag-limited sample, cluster area~1.4Mpc

• All sampling and magnitude cutoffs (R !~14.75 or MV ! -19.9) were mimicked byPoggianti et al.

Jclub - 1 Feb, 08 6

Walk Them Through Issues

• Difference inarea coveredby spectracould result inaperture effects

• A galaxy withan old centerand youngouter radiusshould lie(B-R)tot < 1.4 and(B-R)2”.7 > 1.4

• So, observed spectraldifferences are real and are notresponsible for variations inspectral properties at differentredshifts– mag conversion & lum brightening

Jclub - 1 Feb, 08 7

Massive Loads of Grading

MORPHS• 20% of total

population luminousk+a spectra

• Emission-linegalaxies 26.5% ±3

• K-type ~51% ±4• Can only study the

bright end

Poggianti et al.• No luminious k+a

spectra detected atsimilar luminosity

• Overall emission-linegalaxies 9.4% ±5

• K-type 90.6% ±17• 23 faint k+a galaxies,

where– 13 secure, 10 more

uncertain "

Jclub - 1 Feb, 08 8

Blind them with pretty pictures…

• Balmer lines: H#, H$, H%, H&, H!, H'

Jclub - 1 Feb, 08 9

Jclub - 1 Feb, 08 10

• Only included galaxies with R < 19• Below we see that k+a make up

10-15% of the faint dwarfpopulation

• “?” meansthose galaxiesunable to beclassified

• Thoseuncertain areincluded insidethe ( )

Jclub - 1 Feb, 08 11

vavg= 8120±709 km/s

vavg= 6992±761 km/s

Jclub - 1 Feb, 08 12

Look at the Sky• No general preferential

k+a positioning• Note placement of blue

k+a’s (strong H! EWs)– Higher mean radial vel

• Strength of lines andcolor mean SF stopped.05-.3Gyr ago– Compared to .7-1.5Gyr

• Distinction indicatesquenching of astarburst (mechanism?)

Western

structure

Jclub - 1 Feb, 08 13

Strong k+a

Weak k+a

Speedy dwarfs

T < 8keV

8keV < T < 10keV

T > 10keV

Caused by infall

via compression

or shock waves

Jclub - 1 Feb, 08 14

Starburst galaxies

Sfing (spiral-like)

Emission-line (?)

Jclub - 1 Feb, 08 15

Complain (a lot)

• Problem: other studies biased towards early-typegalaxies, not mag-limited

• Luminous k+a galaxies present in clusters at high-zbut absent in Coma– Not much environmental change from z = 0-0.5

• Instead cosmic “downsizing effect” (infall)– Gas reservoir for later SF created by background radiation?

– Since less massive galaxies more easily disrupted, they musthave been in different past environments to still survive

• Probably late-SF/starbursting dwarfs becomingsph/elliptical dwarfs due to cluster environment

Jclub - 1 Feb, 08 16

Thank You! !god, it’s only for a few years

Appreciation for Prof. Jansen forexplaining the “k+a” nomenclature,my classmates for not falling asleep,Extreme Bean coffee shop,Papa Johns, Prof. Rhoads forcanceling class on Monday,Wikipedia, iTunes, & Tatertot