1. Sandage 1986 Roughly speaking, the Hubble sequence is also a sequence in star formation histories. HUBBLE TYPES and STAR_FORMATION HISTORIES

2. 1. Star formation from fossil records: why useful and what for STAR FORMATION HISTORY OF NON-STARFORMING GALAXIES

3. Indicators of ongoing star-formation activity - Timescales Emission lines < 3 x 10 7 yrs UV-continuum emission it depends… FIR emission < a few 10^7 (but…) Radio emission as FIR (?) (Could be higher: relativistic electrons have lifetimes ≤ 10^8 yr)

4. THE IMPORTANCE OF FOSSIL RECORDS: Goal: understanding galaxy formation and evolution Going to higher-z is not always the solution….problem of connecting progenitors and descendants The evolutionary history of a galaxy is written in its stars, therefore in the light they emit – the light of all stars together form the galaxy integrated spectrum A method to reconstruct the past star-formation history

5. All these techniques are based on one single fact: that STARS OF DIFFERENT AGES HAVE DIFFERENT SPECTRAL ENERGY DISTRIBUTIONS (in shape and lines)

6. Young populations are bright Young populations are hot Old populations are faint Old populations are cool

7. SPECTROPHOTOMETRIC MODELS Simply adding up the light of all stars: a Single Stellar Population (SSP) stellar IMF Monochromatic luminosity emitted by a star with mass m, metallicity Z and age T

9. SPECTROPHOTOMETRIC MODELS Simply adding up the light of all stars: a galaxy (composite spectrum)

10. The oldest galaxies at any redshift Color-Magnitude sequence: zero-point, slope and scatter passive evolution of stellar populations formed at z>2-3. Slope is primarily driven by mass-metallicity relation. Morphologically (HST)-selected Es and S0s (Bower et al. 1992, Aragon-Salamanca et al. 1993, Rakos et al. 1995, Stanford et al. 1995, 1996, 1997, 1998, Schade et al. 1996, 1997, Ellis et al. 1997, Lopez-Cruz 1997, Kodama et al. 1998, Barger et al. 1998, van Dokkum et al.1998, 1999, 2000, 2001, Gladders et al. 1998, de Propris et al. 1999, Terlevich et al. 1999, 2001, Vazdekis et al. 2001, Andreon 2003, Merluzzi et al. 2003; Rosati et al. 1999, Lubin et al. 2000, Stanford et al. 1998, 2002, Kajisawa et al. 2000, van Dokkum et al. 2000, Blakeslee et al. 2003) Fundamental Plane, Mass-to-Light ratios and Mg-sigma relation (van Dokkum & Franx 1996, Kelson et al. 1997, 2000, 2001, van Dokkum et al. 1998, Bender et al. 1996, 1998, Ziegler & Bender 1997, Ziegler et al. 2001, Holden et al. 2004) Bright-end of K-band (mass) luminosity function (Kodama & Bower 2004, Toft et al. 2004, Strazzullo et al. 2006) Blakeslee et al. 2003 Z = 1.24

11. The big problem for hierarchical models like CDM: For the biggest galaxies, the halos continue to merge until late times, z~1 or even z~0.5. This is why a picture in which ellipticals were made by merging spirals at late times seemed the “perfect fit.” However, the stars of elliptical galaxies (and all big spheroids = bulges) really are old, and they are enhanced in alpha-elements compared to spirals. The stars in spheroids seem to be uniformly old, very few, or none of them, are young. Dressler

12. Passive Galaxies: The Classical Picture Passive Galaxies: The Classical Picture Homogeneity of Cluster E/S0 U-V Colors z  0.0z  0.5 (HST) Virgo & Coma:  (U-V) o < 0.05 (Bower, Lucey & Ellis 1990, Bower et al 1998) Morphs: = 0.5 sample:  (U-V) o < 0.07 (Ellis et al 1997)

13. Ellis et al. 1997 (ApJ 483,582) V-I I 814 V-I 0.00.20.4-0.2-0.4 (Rest frame U-B) Kuntschner & Davies (1998 MNRAS, 295, L33) Kelson et al. 2001 UV scatter Fundamental plane Spectral signatures

14. Universal relation for Es and S0s (Sandage & Visvanathan 1978) Scatter dominated by observational errors (Bower et al 1990, Bower et al 1998)  (U-V) is sensitive probe of decline rate of MS component (Buzzoni 1989)  uniform star formation history: synchronisation of recent activity or old stellar population z F > 3 Tight color-luminosity relations: stars are old z  0 z  0.5 U-V (U-V) 0

15. Unfortunately, degeneracy between age and metallicity -

16. Young populations are bright Young populations are hot Metal poor populations are hot Old populations are faint Old populations are cool Metal rich populations are cool

17. Integrated Colors Young populations are BLUE Metal poor populations are BLUE Old populations are RED Metal rich populations are RED From Colors AGE, Z but degenerate…

18. Spectral Indices Broad Band Colors are affected by the AGE-METALLICITY DEGENERACY Spectral indices have been introduced to overcome this problem

19. Kuntschner & Davies 1997

20. Lick Indices Measurement: EW, e.g.: MAG, e.g.:

21. SSP Lick Indices: an example Metallic line strenghts increase with both AGE and Metallicity Hβ gets weaker as age increases and as Metallicity increases Use combination of metallic and Balmer line strengths to solve the AGE-METALLICITY degeneracy

22. A Balmer line versus a metallicity indicator….

23. In this way, obtaining luminosity-weighted ages and metallicity (~epoch of most recent star formation)

24. Alpha elements overabundance in Es Worthey, Faber & Gonzales 1992: At given Fe index, the data Mg index is stronger than the model predictions Interpreted as a supersolar Mg/Fe ratio Among various possibilities: Short Formation timescales for Es Solution: Find a combination of indices that does not depend on overabundance (eg Thomas et al., Tantalo et al., et al.)

25. RELATED ISSUES AND PROBLEMS: In practice, galaxies are not SSPs !!! (again, degeneracies…) Dust normally considered negligible in non-star- forming galaxies Emission can get in the way: filling of Balmer lines Slit effects Never trust absolute ages, only relative ones You get what you’ve put in: model limits There is not a “best method” in an absolute sense. It depends on resolution and S/N of the data

26. Fasano et al. 2000 N S0 /N E 0 0.6 Redshift Dressler et al. 1997 EVOLUTION OF S0s

27. Stellar populations as a function of galaxy morphology Reality of E-S0 differences “confirmed” from spectroscopy and colors (Kuntschner & Davies 1998 in Fornax, Terlevich et al. 1999 in Coma, Smail et al. 2001 in A2218, Poggianti et al. 2001 in Coma, Thomas 2002 PhD Leiden ENACS) but not all studies find differences (Ellis et al.1997, Jorgensen 1999, Lewis et al. 2001, Ziegler et al. 2001)

28. Fornax cluster -- Kuntschner & Davies 1998 (also Coma cluster Poggianti et al. 2001b, Abell 2218 Smail et al. 2001) Ellipticals in clusters terminated their SFH at high redshift In contrast, a significant fraction of the S0 galaxies finished forming stars more recently The age of ellipticals

29. Poggianti et al. 2001b

30. Jones, Smail & Couch 2001

31. Stellar populations as a function of galaxy morphology Reality of E-S0 differences “confirmed” from spectroscopy and colors (Kuntschner & Davies 1998 in Fornax, Terlevich et al. 1999 in Coma, Smail et al. 2001 in A2218, Poggianti et al. 2001 in Coma, Thomas 2002 PhD Leiden ENACS) but not all studies find differences (Ellis et al.1997, Jorgensen 1999, Lewis et al. 2001, Ziegler et al. 2001) : due to delay between evolution of SF and morphology? (Poggianti et al. 1999) – or to the different luminosity distribution of samples? (P. et al. 2001)

32. Trends with galaxy mass/luminosity Poggianti et al. 2001a

33. Poggianti et al. 2001 Differences Es vs S0s **not** visible at the brightest magnitudes

34. Poggianti et al. 2001a empty circles: lum. wei. age > 9 Gyr z=1-1.5 crosses: 3 < age < 9 Gyr filled circles: age < 3 Gyr z=0.25 M B >-15.6 -17.3 <-18.6 DOWNSIZING EFFECT

35. THE BUILD-UP OF THE RED COLOR-MAGNITUDE SEQUENCE ESO Distant Cluster Survey, De Lucia et al. 2004

36. De Lucia et al. 2004 ApJL A deficiency of red galaxies at faint magnitudes compared to Coma -- A synchronous formation of stars in all red sequence galaxies is ruled out -- Most luminous galaxies are the first ones to conclude their SF activity - The more luminous, the older their stellar populations,and the higher the redshift of their last SF Downsizing effect: the star formation histories of galaxies are anti-hierarchical The build-up of the CM sequence See Tran et al. 2003 & Poggianti et al. 2004 for downsinzing of the post-starburst cluster population

37. Results: larger galaxies older than smaller ones Kauffmann etal. (2003) Caldwell et al. (2003) Yamada etal. (2005a) VIRGO σ σ Cowie et al. 1996

38. Downsizing-effect Going to lower redshifts, the maximum luminosity/mass of galaxies with significant SF activity progressively decreases. Active star formation in low mass galaxies seems to be (on average) more protracted than in massive galaxies. IN ALL ENVIRONMENTS. The more luminous/massive, the older their stellar populations, the higher the redshift of their last SF activity More massive galaxies on average older, more metal-rich, higher alpha/iron

39. 58% 20% 22% IN NUMBER OF GALAXIES 79% 18% 3% IN TOTAL STELLAR MASS z > 1-1.5 0.25 < z < 1 z < 0.25 Epoch of latest star formation in galaxies in the Coma cluster

40. Stars in cluster ellipticals are old, there seems little doubt, and they also appear to be assembled into mature galaxies very early. But, cluster ellipticals are rarer than those in lower-density environments -- are these “field” ellipticals really all that different (stellar age, assembly age) from cluster E’s?

41. Declining Red Sequence to z=1: Agreement with CDM? COMBO-17 data suggests  3 decline in `red sequence’ luminosity density to z=1: consistent with hierarchical predictions (Bell et al ApJ 608, 752 2004) Color-photometric z’s in COMBO-17Red luminosity density

42. Gemini Deep Deep Survey Glazebrook et al Nature 430, 181 (2004) By contrast, the Gemini DD Survey find an abundance of high mass old objects at redshifts z>1 - in seeming contradiction with the COMBO-17 results to z~1? (Can reconcile these contradictory observations if mass assembly is itself mass-dependent) R-K Redshift

43. McCarthy et al Ap J 614, L9 (2004) Gemini Deep Deep Survey: Spectroscopic Age-dating 20 red galaxies z~1.5, age 1.2 - 2.3 Gyr, z F =2.4 - 3.3 Progenitors have SFRs ~ 300-500 M  yr -1 (sub-mm gals?)

44. “Evolved Galaxies at z>1.5 from the Gemini Deep Deep Survey: The Formation Epoch of Massive Stellar Systems”, McCarthy et al. (GDDS), 2004 ApJ, 614, L9 “Spectra of evolved GDDS galaxies with z > 1.3. The SDSS LRG composite has been overlaid on each spectrum, and an offset has been applied to each, in steps of 10^-18 ergs cm-2 Å-1” “Both composite spectra show strong Mg II 2800, Mg I 2852 absorption and broad spectral features due primarily to Fe II absorption. Overlaid in red is a single-burst Bruzual & Charlot spectral synthesis model with an age of 2 Gyr, solar abundances, and a Salpeter IMF cutoff at 120 Msun” “Conservative age estimates for 20 galaxies with z > 1.3…give a median age of 1.2 Gyr and zf = 2.4. One-quarter of the galaxies have inferred zf > 4. Models restricted to [Fe/H] ~0 give median ages and zf of 2.3 Gyr and 3.3, respectively. These galaxies are among the most massive and contribute 50% of the stellar mass density at 1 < z < 2. …Our results point toward early and rapid formation for a significant fraction of present-day massive galaxies.” Can feedback with hierarchical CDM explain?

45. How much has the red sequence grown since z = 1? Faber et al. (Deep2) -- a factor of 4 growth since z=1, and this includes the brightest (most massive) red galaxies -- need a lot of merging and quenching to accomplish that! Borch et al. (Combo-17) 2006 A&A, 453, 869. “ We find that the total stellar mass density of the universe has roughly doubled since z ~ 1…Intriguingly, the integrated stellar mass of blue galaxies with young stars has not significantly changed since z ~ 1…instead, the growth of the total stellar mass density is dominated by the growth of the total mass in the largely passive galaxies on the red sequence.” Cimatti et al. 2006 A&A 453, L29 -- same conclusion, a factor of two growth in the red sequence, and no growth for the massive systems. Brown et al. 2006 astro-ph 0609584 -- NOAO and Spitzer IRAC survey: “…the stellar mass contained within the red galaxy population has roughly doubled over the past 8Gyr. This is consistent with starforming galaxies being transformed into 4L* galaxies since z=1. “ While red galaxy mergers have been observed, such mergers do not produce rapid growth of 4L* red galaxy stellar masses between z=1 and the present day.”

46. Brown et al. and Cimatti et al. emphasize that, if only a factor of two in mass is added to the red sequence since z~1, and it is mainly in lower luminosity (< 10 11 M sun ) galaxies, then simple “running down” of star formation in disk galaxies, turning them red, can account for the growth. A key point to be resolved, and one that may be telling as to how much the hierarchical picture is in trouble.

47. Post-starburst galaxies: a class apart

48. EW(Hdelta) (4102 A) > 3 A and no line detected in emission Balmer lines in absorption are best indicators of “recent” SF (some more than others)

49. Martins et al. 2005 ONE STAR

51. Martins et al. 2005

52. Gonzalez-Delgado et al. 2005 ONE SSP

53. EW(Hdelta) of an SSP

54. Gonzalez-Delgado et al. 2005

55. Jacopo Fritz 2005

56. EW(Hdelta) (4102 A) > 3 A and no line detected in emission

57. SOME OBSERVED SPECTRA

61. “...these spectra are consistent with an old population mixed with an equal blue luminosity of A stars, which indicates a large burst of star formation 10^9 years before the light left the galaxy.” Dressler & Gunn 1983 An abrupt interruption of the SF activity gives rise to a post- starburst spectrum for ~1-1.5 Gyr after the SF is terminated

62. EW(Hdelta) of an SSP

64. NOMENCLATURE: A ZOO!! E+A galaxies k+a galaxies HDS(Hdelta strong) galaxies Post-starburst/Post-starforming galaxies (PSB/PSF) Balmer-strong galaxies

65. ADVANTAGES: It is a signature that DOES NOT depend on metallicity and abundance ratios Easy to identify them…. DISADVANTAGES: …but difficult to understand the details - Strenght, age and duration of burst highly unconstrained – only lower limits can be placed in most cases

67. ADVANTAGES: It is a signature that DOES NOT depend on metallicity and abundance ratios Easy to identify them…. DISADVANTAGES: …but difficult to understand the details - Strenght, age and duration of burst highly unconstrained – only lower limits can be placed in most cases

68. Emission lines < 5 x 10 7 yrs FIR emission < a few 10^7 (but..) Radio emission as FIR (but…) etc. Spectra w/out emission lines k+a spectra 5 x 10 7 to 1.5 Gyr abs line indices > 1.5 Gyr

69. k+a galaxies Dressler & Gunn 1983, Couch & Sharples 1987, Henry & Lavery 1987, Newberry et al. 1990, Fabricant et al. 1991,1994, Dressler & Gunn 1992, Charlot & Silk 1994, Jablonka & Alloin 1994, Belloni et al. 1995, 1996, Abraham et al. 1996, Barger et al. 1996, Leonardi & Rose 1996, Poggianti & Barbaro 1996, Fisher et al. 1998, Morris et al. 1998, Couch et al. 1998, Balogh et al. 1999, Dressler et al. 1999, Poggianti et al. 1999, Bartholomew et al. 2001, Ellingson et al. 2001, Bekki et al. 2001, Shioya et al. 2001,2002, Tran et al. 2003, Goto 2003, Poggianti et al. 2004, Balogh et al. 2005, Yamauchi & Goto 2005 ~10 Myr to 1.5 Gyr after SF stopped strongest cases need a starburst weak cases also simply truncated SF combination EW-color helps for evol.stage a slow declining SF does not work Recently, Hdelta versus D4 study of SLOAN galaxies (Kauffmann et al. 2003)

70. ABSORPTION-LINE SPECTRA: the smoking guns When first spectra of galaxies in distant clusters, surprise surprise... Spectra with strong Balmer lines in absorption and no emission (E+A/k+a galaxies) – post-starburst/post-starforming galaxies (Dressler & Gunn 1982,1983, Couch & Sharples 1987, Henry & Lavery 1987, Fabricant et al. 1991,1994, Dressler & Gunn 1992, Barger et al. 1996, Belloni et al. 1995, 1996, Abraham et al. 1996, Fisher et al. 1998, Morris et al. 1998, Couch et al. 1998) Larger % in clusters (10-20%) than in field at similar z’s (Dressler et al. 1999, Poggianti et al. 1999, Tran et al. 2003,2004 – as opposed to Balogh et al. 1999) -- SF truncation in clusters --

71. The maximum velocity- dispersion (=mass) of k+a galaxies in clusters decreases towards lower redshifts (Tran et al. 2003) At z=0, in the Coma cluster, observing late star-forming faint galaxies becoming “dwarf ellipticals” About 10% of the dwarf cluster population in the Coma cluster (see also Caldwell et al.’s works, De Propris et al.) Poggianti et al. 2004 Downsizing-effect: evolution of the k+a population in clusters

72. POST-STARBURST GALAXIES  Any process that halts the SF on a short timescale will produce a k+a spectrum (running out of fuel after a SB? Having the ISM removed due to the dense environment?)  Probably different origin in clusters of galaxies and in the field  Complete picture is still lacking, but current scenario: post-SB galaxies in clusters: an important fraction of the luminous galaxy populations at intermediate redshift (15-20%) – low mass galaxies in the nearby universe – an environmentally- related phenomenon, occurring in dense regions post-SB galaxies in the field: locally, a very small fraction of the luminous galaxies (0.1%), probably related to mergers – at high-z, recent studies start to find luminous k+a galaxies