This week at Astro 3303

Transcription

1 This week at Astro 3303 HW #7 is due on Tuesday 2 nd 30-min test on Thurs Apr 5 Same format as before Will focus on material since Feb 28 (but some material is cumulative) Lecture notes are posted. Today: Large scale structure in the universe Groups and clusters of galaxies Quantifying environment Reading: Chapter 6

2 The end is near I will be in Europe Apr I will be in contact most of the time. The grad students will be in charge of A3303. R Apr 12: T Apr 14: R Apr 16: Betsey Manolis Greg

3 Week of April 10: Week of April 17: Week of April 24 : Week of May 1 st : In class presentations First presentation (2-3 min; no slides) Second presentation (2-3 min; we provide 1 slide) Presentation (12 minutes) Who Science topic Facility/mission CMB polarization Dark ages First light Early galaxies Sunyaev-Zel dovich Effect Counting galaxy clusters Baryon acoustic oscillations Weak lensing Type Ia SNe POLARBEAR EDGES/PAPER/MWA JWST ALMA/CCAT Planck Dark Energy Survey BigBOSS LSST WFIRST

4 Week of April 10: Week of April 17: Week of April 24 : Week of May 1 st : In class presentations First presentation (2-3 min; no slides) Second presentation (2-3 min; we provide 1 slide) Presentation (12 minutes)

5 NGC 4258 Moran 2008 Review Has two sets of arms, offset in orientation! Radio/Xray arms shock heated. Powerful jet in core (SMBH) Seyfert II spectrum M SMBH ~ 4 x 10 7 M ʘ VLBA

6 NGC 4258 H 2 0 masers at 22 GHz 22 GHz Angular resolution ~ 200 µas (microarcsec) Spectral resolution ~ 1 km/sec Radial velocity (l.o.s.) = GM/R sin θ where θ is the azimuthal angle in the disk measured from the BH, R is the radial distance from the BH, M is the mass of the BH. Close to l.o.s., sin θ ~ b/r, where b is the impact parameter, so V z ~ b GM/R 3

7 NGC 4258 Over time, masers are tracked as they orbit, and eventually disappear from sight. Their velocities increase by about 8 km/s/yr from 430 km/s to 530 km/s; we only see them when their maser emission is beamed along the l.o.s. Inner disk radius is 8.3 mas = 0.29 pc from the central BH.

8 NGC 4258

9 Measure x,y, v los, a los, & proper motions, x y highv highv Acceleration Distance v los 2 M/D highv M/D highv dv los /d [M/D sys3 ] 1/2 sys sys a los v 2 / D sys D M or V. θ Proper Motion Distance ~ v t /D (M/D) 1/2 /D sys 1/2 D M

10 Large scale structure in the universe Galaxies trace hierarchical structures: groups, clusters and superclusters The principal differences between a group and a cluster is the number (N) of members the total mass of the group/cluster the velocity dispersion *: of order ~250 km/s for a group and perhaps ~ km/s for a rich cluster The typical radius of a group or cluster is ~ 2 Mpc = 6.7 million light years *velocity dispersion: typical orbital velocity of a galaxy in the group/cluster

11 Groups and clusters are roughly the same size (radius = 2 Mpc) The basic difference is the number of galaxies = > density of galaxies (number per volume) Morphological makeup Presence of hot gas Groups and clusters

12 Morphological segregation Ellipticals Spirals Smooth light distribution Arms, disk, bulge Brightest stars are red Brightest are blue Little/no star formation On-going star formation Little/no cool/cold gas Molecular + atomic gas Random motions Circular rotation in disk Found in cluster cores Avoid cluster cores S0 (lenticular): Spiral-like: disk+bulge, rotation Elliptical-like: little gas/star formation; no spiral structure

13 Elliptical versus Spiral Galaxies Morphological segregation: Initial conditions or evolution over time??? 100% Percent of total Percent galaxy of population total population 80% 60% 40% 20% E + S0 Spiral Low density Field High density Cluster

14 Coma Cluster = A1656 cz ~ 7000 km/s Often used as prototype rich cluster

15 X-rays in clusters

16 Clusters contain 100s to 1000s of galaxies per Mpc -3 as well as hot (Temp~10 8 K) gas, detected as X-ray emission. Clusters of Galaxies

17 Clusters of galaxies

18 Abell Catalog of Rich Clusters Abell 1958, ApJ Suppl 3, 211 (2712 clusters) Abell et al, 1991 ApJ Supp 70, 1 (+ south = 4073) richness class & distance class (now confirmed by redshifts) A cluster must contain > 50 members that are not more than 2 magnitudes fainter than the 3 rd brightest A cluster must be sufficiently compact that its >50 members are within a given radial distance (R A ) of its center. R A is arbitrary so long as it is the same for all clusters. Abell Radius R A ~ 1.5 h -1 Mpc Virgo is not an Abell cluster Coma is Abell 1656

19 Compact Groups: Hickson 1982 & 1997 (ARAA 35, 357) High density but low mass/lum Richness: N>3 with m<m 1 +3mag Isolation: R neighbor >3R group Compactness: G <26 mag/arcsec 2 (selected off of red plates, so bias towards early types) May be stage in evolution to cluster core, field early type, fossil group, or dry merger remnants Strong local density enhancement but velocity dispersion similar to loose groups (~250 km/s) Condensation w/in looser, prolatelike elongated systems; members on orbits aligned with long axis e.g. Tovmassian et al 2006 A&A 456, 839

20 Fossil Groups: e.g Jones et al. 2003, MNRAS 343, 627 Idea: Fossil groups are end result of galaxy merging within a normal group, leaving X-ray halo Identified by combination of rather high L X and very low richness, with single galaxy with L > L * Extended X-ray source with L X > h 50-2 erg/s (comparable to Virgo cluster) This limit precludes individual galaxies Optical counterpart is a bound system of galaxies with m 12 > 2.0 mag (difference in abs mag of 1 st and 2 nd brightest galaxies, within half projected virial radius) This limit insures the brightest galaxy dominates

21 Poor clusters: e.g MKW: Morgan, Kayser & White 1975, ApJ 199, 545 AMW: Albert, White & Morgan 1977, ApJ 211, 309 WBL: White et al. 1999, AstroJ 118, 2014 Surface density enhancements in CGCG (nearby) Contain dominant giant elliptical galaxy Exhibit a range of L X (wider than fossil groups) But fewer members overall than Abell clusters

22 X-ray properties of rich clusters

23 Masses of clusters See also Heisler, Tremaine & Bahcall (1985) for alternative mass estimators dp M(<r) = -G dr r 2

24 L X 4.4 L X T X 3 Close relations between X- ray L and T and velocity dispersion of cluster T X 2 T(keV) = x 10-9 erg 1.38 x erg K -1 = 1.16 x 10 7 K from Mulchaey (2000)

25 Global correlations in clusters

26 X-ray observations of hot ICM in clusters Clusters of galaxies are the most common bright extragalactic X-ray sources. Cluster have very high L X ~ erg s -1. The range of L X is very high. Clusters are the most luminous class of X-ray sources, except for quasars. X-ray sources associated with clusters are extended, typical R X ~200 kpc to 3 Mpc. Clusters show X-ray spectra that show no strong evidence of low E photoabsorption. X-ray emission from clusters is not time-variable. Thermal bremsstrahlung spectrum n e exp (-h /kt) 4 ( ) = 6.8 x T n e (r=0) ~ 10-3 cm -3, T~ 10 8 K

27 Hot gas in clusters Rosati ARAA Sarazin 1988 RevModPhys Can be < t Hub

28 X-ray observations of hot ICM in clusters X-ray distribution centered on cluster center, as determined by the galaxy distribution, or on active galaxy in the cluster. Favored model: isothermal, hydrostatic Both gas and galaxies are assumed to be: 1. Isothermal 2. Bound to cluster 3. In equilibrium Galaxies assumed to have an isotropic velocity dispersion, but the gas and galaxies are NOT assumed to have the same velocity dispersion Then m p r 2 kt gas gas gal where = mean molecular weight in amu m p = mass of proton r = 1-D velocity dispersion T gas = gas temperature in K

29 X-ray observations of hot ICM in clusters Assume a galaxy distribution has a King analytic form (truncated isothermal sphere Space density: n(r) = n o [ 1 + (r/r c ) 2 ] -3/2 Surface density: (b) = o [ 1 + (b/r c ) 2 ] -1 o = 2 n o r c Then the X-ray surface brightness I X goes as I X (b) [ 1 + (b/r c ) 2 ] -3 + ½ Typical fits to X-ray SB yield < > ~ 0.65 => gas more extensively distributed than galaxies R c ~ (0.1 to 1.2 Mpc) => wide range Cooling flows: If the rate of cooling of the IC gas is sufficiently rapid, then gas may cool and flow into the center of the cluster (Sarazin 1986). Evidence 1. Peaks in soft Xray SB at cluster center 2. Measurement of inverted temp gradient dt/dr > 0 3. Soft X-ray line emission of low ionization lines at center (T ~ K at center)

30 Sunyaev-Zel dovich effect

31 Gas and Galaxies in the Virgo Cluster baryons : the heavy ones (protons, neutrons, electrons, atoms etc) The mass of the hot ICM gas is ~5X more than the combined mass of all the stars in all of the galaxies! But what is the actual mass of the cluster itself?

32 Hot Gas in the Virgo Cluster Extended X-ray emission implies hot Intra Cluster Medium => temperature is 100 million degrees Kelvin! The cluster contains thousands of galaxies within its radius of 2 Mpc (7.5 degrees) How can we measure its mass??? (How can we measure the mass of an object?)

33 Estimating the Mass of the Virgo Cluster Estimating the mass of a cluster Observe the cluster s EXTENT. Observe the redshifts of many cluster galaxies; figure out which ones are in the cluster (not in the foreground or background) How much mass is required to keep the galaxies moving with those speeds from escaping? Virgo Cluster Catalog ~2000 objects Based on morphological appearance Largely confirmed by redshift measurements Distance ~ 17 Mpc Binggeli, Sandage & Tammann 1985, AJ 90, 1681

34 Virgo cluster Each point represents a galaxy. Each point is plotted at the coordinates of the galaxy: Right Ascension and Declination The red X marks the location of the giant elliptical galaxy Messier 87 (M87). A map, on the sky, of all the galaxies in the Virgo Cluster Catalog with measured redshifts (= Doppler shifts, radial velocities).

35 PE #17: The Virgo cluster Why do we draw R.A. increasing to the left? What do we mean by heliocentric velocity Why do some galaxies have negative velocities?

36 Determining cluster membership Examine how the observed heliocentric velocities are distributed as a function of radial distance from the central position. We expect the cluster members to have about the same redshift (with a dispersion of km/s) so the objects offset by 1000s of km/s cannot be members => they are clearly separated in this plot. Background objects Here: a more distant cluster than Virgo Foreground objects Virgo is tricky because it is so close to us => harder to figure out membership

37 Cluster membership Why do there seem to be more galaxies at higher velocities than at lower ones?

38 PE #17: Virgo Mean heliocentric velocity ~ 1100 km/s Velocity spread ~ 1200 km/s (full width) characteristic radial velocity ~ 600 km/s But we actually need the 3-dimensional velocity so multiply by sqrt(3)

39 The back-of-the-envelope mass of Virgo: G = 6.67 X 10-8 dyne cm 2 gm -2 1 pc = X cm 1 solar mass = X gm Virial mass of Virgo cluster = 2 2 Mpc x (1.7 x 600 km/s) 2 G 2x2 Mpc x10 6 pc/mpc x 3.086x10 18 cm/pc (1.7x600 km/s x10 5 cm/km) x 10-8 (1.02x10 8 ) 2 = 1.04x10 16 = 2 x 2 x x 1.04x10 ( ) = 6.67 x x gm 2.0 x gm/solar mass = 12.8 x x 10-8 = 9.5 x solar masses

40 The Virgo Cluster: Bad things are happening

41 Elliptical versus Spiral Galaxies Morphological segregation: Initial conditions or evolution over time??? 100% Percent of total galaxy population Percent of total population 80% 60% 40% 20% E + S0 Spiral Low density Field High density Cluster

42 Morphology-clustercentric radius relation

43 Interactions, Tides and Mergers Galaxy - galaxy interactions Galaxy ICM interactions

44 Morphological alteration mechanisms Gravitational mechanisms Galaxy-galaxy interactions Direct collisions Tidal encounters Mergers Galaxy-cluster interactions Harassment (multiple rapid tidal encounters) GRAVITY Galaxy-intracluster medium interactions Thermal evaporation Ram pressure sweeping INTRACLUSTER GAS

45 Tides and collisions Disturbed morphological appears: bridges, tails, asymmetry Gaseous material accreted by gas-poor galaxy induces star formation in otherwise dormant galaxy => starburst Disturbed material (velocity as well as location changes) may not be able to resist gravitational attraction of supermassive black hole => falls towards black hole => heated/collides with other material => photons emitted => luminosity!

46 N-body simulations: binary stars 1. Adopt the masses of the 2 objects (so here N=2) 2. Adopt characteristics of the orbits (eccentricity, inclination, orientation) 3. Apply the laws of gravity to predict the relative positions of the two objects after every time step.

47 N-body simulations: Sun-Earth-Moon 1. Adopt the masses of the 3 bodies (so here N=3) 2. Adopt characteristics of the orbits (eccentricity, inclination, orientation) 3. Apply the laws of gravity to predict the relative positions of the N objects after every time step.

48 Toomre & Toomre 1972 The galaxy s mass is concentrated at a point The outer disk particles are arranged in 5 rings They do not interact with each other (no self-gravity) All passages involve two galaxies that have a close, slow moving parabolic approach Each time unit is 100 million years Although much more sophisticated codes exist today, T&T72 demonstrated the overall damage done by tides.

49 Got this far didn t finish PE17; jumped ahead as prelude