The Role of Dwarf Galaxies in the Formation of Stellar Halos:

Transcription

1 The Role of Dwarf Galaxies in the Formation of Stellar Halos: Chemical Abundance Analysis of Extragalactic Red Giants Evan Kirby UC Santa Cruz Qualifying Examination / Dissertation Topic Defense June 4, 2007

2 Outline Motivation Abundance gradients in M31 des Existing low-res metallicity measures New low-res metallicities Future applications (spectral coaddition) Beyond the Local Group Single-line redshifts Low luminosity galaxies in DEEP2 Lyα emitters Timeline 2/46

3 Have You Seen Me? MOORE ET AL Klypin et al /46

4 N( > vcirc) Missing Satellites Klypin et al vcirc (km/s) 4/46

5 Number mag-1 Missing Satellites Found MV 5 log h70 Somerville 2002 Bullock & Johnston /46

6 MV More Missing Satellites Found log (rh/pc) Belokurov et al /46

7 Venn et al V (km/s) N( < [Fe/H]) [Mg+Ca+Ti/3Fe] [Fe/H] Chemistry is History Helmi et al [Fe/H] [Fe/H] 7/46

8 Chemistry is History 8/46 Font et al. 2006

9 <[Fe/H]> S0 (mag arcmin-2) Another Neighborhood R (kpc) Kalirai et al MV McConnachie & Irwin /46

10 Gradients in M31 dsphs Harbeck et al /46

11 Gradients Reflect Star Formation [Fe/H]spec [Fe/H]spec Mateo 1998 r (arcmin) r (arcmin) Kirby et al (in prep) 11/46

12 Gradients in NGC 205 [Fe/H]spec velocity (km s-1) Mateo 1998 semi-major axis (arcmin) Geha et al r (arcmin) Kirby et al (in prep) 12/46

13 I Funky Photometry R I 13/46

14 I Funky Photometry R I 14/46

15 I Funky Photometry R I 15/46

16 [Fe/H]phot [Fe/H]spec [Fe/H]spec [Fe/H]spec r (arcmin) r (arcmin) [Fe/H]phot r (arcmin) [Fe/H]phot 16/46 [Fe/H]spec [Fe/H]spec [Fe/H]spec [Fe/H]phot [Fe/H]phot [Fe/H]phot

17 Photometric Metallicity I R I Isochrones from VandenBerg, Bergbusch, and Dowler 2006 Must assume age and [α/fe] 17/46

18 Statistical Constraints 18/46 Tom Brown, STScI

19 Statistical Constraints 19/46 Tom Brown, STScI

20 Spectroscopic Metallicity [Fe/H]HDS Ca triplet calibration by Rutledge, Hesser, and Stetson 1997 Uses high-dispersion spectroscopy by Carretta & Gratton 1997 <W'> Rutledge, Hesser & Stetson /46

21 Data Set M31 dwarfs NGC 147 NGC 185 NGC 205 And I And II And III And X And XIV MW dwarfs Leo I M31 halo up to 165 kpc 90 ~100 21/46

22 Signal-to-Noise 22/46

23 Visible Lines 23/46

24 Visible Lines 24/46

25 Spectral Synthesis Ingredients atmospheric parameters from photometry (Trader Joe's): Teff, log g, initial [Fe/H] line lists (CostCo): wavelength, excitation potential, log (gf) Recipe Kurucz LTE atmosphere, MOOG velocity shift, telluric aborption instrumental smoothing continuum division 25/46

26 Teff Teff Color Temperature color Ramírez & Meléndez /46

27 Instrumental Resolution 27/46

28 Arcturus Synthesis atmospheric parameters and abundances from Peterson, Dalle Ore, & Kurucz /46

29 Iterative [Fe/H] 29/46

30 Evolution of a Spectral Synthesis DEIMOS spectrum of a star in a Leo I, S/N = 36 30/46

31 Evolution of a Spectral Synthesis MOOG synthesis 31/46

32 Evolution of a Spectral Synthesis MOOG synthesis 32/46

33 Evolution of a Spectral Synthesis velocity shift 33/46

34 Evolution of a Spectral Synthesis telluric absorption 34/46

35 Evolution of a Spectral Synthesis instrumental smoothing 35/46

36 Evolution of a Spectral Synthesis continuum division 36/46

37 Evolution of a Spectral Synthesis comparison to observed spectrum 37/46

38 Evolution of a Spectral Synthesis after four iterations 38/46

39 Spectral Fitting 2 cross-correlation or χ minimization dependent on hard-to-model line profiles pseudo-equivalent widths less dependent on instrumental resolution espec 39/46

40 ΔCa II [Ca/H] [Ca/H] from the Ca II Triplet W' Bosler, Smecker-Hane, & Stetson /46

41 [Fe/H]CaT Metallicities in Leo I [Fe/H]phot 41/46

42 [Fe/H]CaT First Ever Low-Res [Ca/Fe] [Fe/H]MOOG 42/46

43 [Ca/H] First Ever Low-Res [Ca/Fe] [Fe/H]MOOG 43/46

44 Things to Work On grid of synthetic spectra to minimize χ2 in {[Fe/H], Teff, log g, ξ} space (i.e., Allende Prieto et al. 2006) better EW measurements need high-resolution stars to compare to M107: 16h33 (visible from Keck II in the west in dusk twilight on Oct 11/12 DEIMOS observing run) 44/46

45 The Future: Coaddition flux rest wavelength (Å) coadd stars of similar photometric properties coadd tens of M31 stars to approximate Leo I spectral quality important to coadd synthetic spectra exactly the same as observed spectra 45/46

46 Timeline Aug 2007 UMich (Gnedin), The Globular Clusters - Dwarf Galaxies Connection Aug-Sep submit paper with Marla on de radial abundance gradients Sep Sawicki et al. Lyα paper Nov draft of updated low L paper Dec Hayama/Subaru conference (poster) Dec-Feb 2008 Majewski (?) et al. M31 surface brightness profile paper Jan AAS, Austin (poster), visit Chris Jan Leo I abundance paper Feb submit low L paper fall job talks Dec Paper I on abundances in M31 (satellites only?) Jan 2009 AAS, Long Beach (dissertation talk) spring Paper II on abundances in M31 (satellites+halo?) Jun defend thesis 46/46 Jul-Aug get married

47 The Role of Dwarf Galaxies in the Formation of Stellar Halos: Chemical Abundance Analysis of Extragalactic Red Giants Evan Kirby UC Santa Cruz Qualifying Examination / Dissertation Topic Defense June 4, 2007 committee: Raja Guhathakurta, chair Sandy Faber Connie Rockosi Chris Sneden

48 Outline Motivation Abundance gradients in M31 des Existing low-res metallicity measures New low-res metallicities Future applications (spectral coaddition) Beyond the Local Group Single-line redshifts Low luminosity galaxies in DEEP2 Lyα emitters Timeline 2/46 motivation: 8 slides, ~7 minutes gradients: 5 slides, ~15 minutes exisitng low-res metallicities: 5 slides, ~5 minutes full-spectrum low-res metallicities: 23 slides, ~40 minutes coaddition: 1 slide, ~3 minutes beyong the LG: 3 separate presentations, ~5 minutes each timeline: 1 slide, ~5 minutes

49 Have You Seen Me? MOORE ET AL Klypin et al /46 cosmological simulations predict a larger number of dwarf satellites than is observed around the MW and M31

50 N( > v circ ) Missing Satellites Klypin et al vcirc (km/s) 4/46 specifically, there are many more DM dsphs in the simulations than luminous dsphs in nature

51 Number mag -1 Missing Satellites Found MV 5 log h70 Somerville 2002 Bullock & Johnston /46 likely, there are many DM dsphs that didn't form stars because they were ionized before they had the chance semi-analytic models that track DM and luminous matter can reproduce satellite number counts assuming small halos cease star formation after reionization and even smaller halos never accrete gas at all

52 MV More Missing Satellites Found log (rh/pc) Belokurov et al SDSS finding many ultra-faint subdwarfs number of And dsphs is up to XVI 6/46

53 [Mg+Ca+Ti/3Fe] V (km/s) Venn et al N( < [Fe/H]) [Fe/H] Chemistry is History Helmi et al [Fe/H] [Fe/H] 7/46 discrepancy between halo and dsph chemical abundances [α/fe] is closer to solar in dsphs: more extended star formation than halo no [Fe/H] < -3 stars found in dsphs, unlike halo

54 Chemistry is History 8/46 Font et al abundance tracking in SAMs shows that smaller substructure has older-looking metallicity you just don't see surviving satellites with high [α/fe] because they have been forming stars somehow for a long time

55 <[Fe/H]> S 0 (mag arcmin -2 ) Another Neighborhood R (kpc) Kalirai et al MV McConnachie & Irwin /46 M31 halo looks a lot like the MW halo, but the inner spheroid is metal-rich compared to the MW furthermore, the dsphs in M31 are dimmer and lower surface brightness than in the MW M31 is more massive, and the DM structure should be more massive on all scales, meaning the dsphs would have higher velocity dispersion and be puffier it's worth studying another neighborhood

56 Gradients in M31 dsphs Harbeck et al /46 while almost all MW dsphs show age or metallicity gradients via HB morphology, And II, III, V, and possibly I show no gradient; only And VI does in all cases with gradients, the RHB stars are more centrally concentrated than the BHB stars, meaning that the metal-rich, more recently formed population is at the center star formation happens where the gas is dense, which is at the center radial gradients mean prolonged star formation

57 Gradients Reflect Star Formation [Fe/H] spec [Fe/H] spec Mateo 1998 r (arcmin) r (arcmin) Kirby et al (in prep) 11/46 SFHs of dwarfs are interesting not only because dwarfs may build up the halo, but in and of themselves, it is interesting to study star formation on the smallest scales I detect a gradient in NGC 185, but not 147 could be because NGC 185 has had a small recent episode of star formation

58 Gradients in NGC 205 [Fe/H] spec velocity (km s -1 ) Mateo 1998 semi-major axis (arcmin) Geha et al r (arcmin) Kirby et al (in prep) 12/46 NGC 205 tidally disturbed evidence of present-day star formation in the inner regions no evidence of radial gradient

59 I Funky Photometry R I 13/46 CMDs from different CCDs are disjoint but there's M31 contamination I've done the best I could to correct the color offset with the dwarf wall could be a magnitude-dependent color term as well

60 I Funky Photometry R I 14/46 compare this CCD on the northwest of NGC

61 I Funky Photometry R I... to this adjacent CCD on the southwest 15/46

62 phot [Fe/H] spec r (arcmin) r (arcmin) [Fe/H] spec [Fe/H] spec [Fe/H]phot [Fe/H] [Fe/H] phot [Fe/H] spec [Fe/H] phot [Fe/H] spec [Fe/H] spec r (arcmin) [Fe/H]phot [Fe/H]phot 16/46 photometric and spectroscopic metallicities are completely independent, and they don't always agree a correlation between the two is evidence of an intrinsic metallicity spread regardless of the problems, both metallicity measures support the existence of a gradient in 185 and the lack thereof in 147 and 205

63 Photometric Metallicity I R I Isochrones from VandenBerg, Bergbusch, and Dowler 2006 Must assume age and [α/fe] 17/46 photometric metallicities obtained by interpolating between monometallicity isochrones on the RGB isochrones from stellar structure models checked against GGCs must assume DM, age, [α/fe]

64 Statistical Constraints 18/46 Tom Brown, STScI high-quality CMDs for M31's stellar halo available possible to constrain ages and metallicities helps pin down [Fe/H]phot

65 Statistical Constraints 19/46 Tom Brown, STScI even possible to give SFR as a function of age for different metallicity populations!

66 Spectroscopic Metallicity [Fe/H] HDS Ca triplet calibration by Rutledge, Hesser, and Stetson 1997 Uses high-dispersion spectroscopy by Carretta & Gratton 1997 <W'> Rutledge, Hesser & Stetson /46 most common spectroscopic metallicity from R97 inherent assumption of [Ca/Fe] when using the CG97 linear calibration R97b: We have no a priori reason to espect how W', an empirical line-strength measure, should be related to [Fe/H], and it is unclear which, if either, [Fe/H] scale to trust. also from R97b: Caution perhaps considerable may be advisable when using W' as a surrogate for metallicity, especially for systems where ranges in age and metallicity are likely. R97b further warn that, while age ranges do not affect CaT metallicities in GGCs, they may be important in dsphs there are other parameters that go into a line than abundance (temperature, gravity)

67 Data Set M31 dwarfs NGC 147 NGC 185 NGC 205 And I And II And III And X And XIV MW dwarfs Leo I M31 halo up to 165 kpc 90 ~100 21/46 many spectra to work with, but they are of variable quality

68 Signal-to-Noise 22/46 S/N defined the same way as in R97a, by measuring the mean deviation in two windows redward of the CaT largely free of lines and telluric absorption

69 Visible Lines 23/46 despite the fact that most abundance work is done blueward of Hα, this red/nir spectrum has many useful lines

70 Visible Lines 24/46 zoom-in on line-rich CaT region

71 Spectral Synthesis Ingredients atmospheric parameters from photometry (Trader Joe's): Teff, log g, initial [Fe/H] line lists (CostCo): wavelength, excitation potential, log (gf) Recipe Kurucz LTE atmosphere, MOOG velocity shift, telluric aborption instrumental smoothing continuum division 25/46 Trader Joe's and CostCo may have good return policies, but I'm stuck with what the photometry and linelists hand me

72 T eff T eff Color Temperature color 26/46 Ramí Ramírez & Melé Meléndez 2005 V-I and [Fe/H] are needed to estimate effective temperature mostly dependent on V-I

73 Instrumental Resolution 27/46 spectral resolution extremely important; it affects line shapes continuum levels hence equivalent widths visibility of lines Ifit Gaussians to arc lamp lines and then fit a hyperbola to their FWHMs then I smoothed according to the hyperbolic function

74 Arcturus Synthesis atmospheric parameters and abundances from Peterson, Dalle Ore, & Kurucz /46 demonstration that I can synthesize a real spectrum the observed lines that are not in the synthetic spectrum must be because my line list does not include those lines

75 Iterative [Fe/H] 29/46 my proposed procedure for measuring [Fe/H] from DEIMOS spectra

76 Evolution of a Spectral Synthesis DEIMOS spectrum of a star in a Leo I, S/N = 36 30/46 object 20198

77 Evolution of a Spectral Synthesis MOOG synthesis 31/46 five syntheses around the photometric [Fe/H]

78 Evolution of a Spectral Synthesis MOOG synthesis 32/46 picking just the synthesis with the photometric [Fe/H]

79 Evolution of a Spectral Synthesis velocity shift 33/46 shifting according to the observed velocity of the science spectrum, plus an additional crosscorrelation to the lines in the CaT region

80 Evolution of a Spectral Synthesis telluric absorption 34/46 add telluric absorption measured from a hot star with the DEIMOS longslit

81 Evolution of a Spectral Synthesis instrumental smoothing 35/46 smooth according to the instrumental resolution measured from the arc lamp lines this doesn't account for seeing or PSF!

82 Evolution of a Spectral Synthesis continuum division 36/46 divide by continuum smooth spectrum in a 67 Å boxcar window 5 iterations of 2-sigma clipping

83 Evolution of a Spectral Synthesis comparison to observed spectrum 37/46 the fit isn't great, but the CaT lines are very hard to model

84 Evolution of a Spectral Synthesis after four iterations 38/46 this is the final synthetic spectrum with the value of [Fe/H] as determined the lines whose pseudo-ew were measured are marked

85 Spectral Fitting cross-correlation or χ2 minimization dependent on hard-to-model line profiles pseudo-equivalent widths less dependent on instrumental resolution espec 39/46 I'm leaning toward measuring EWs from the synthetic spectrum instead of pixel-to-pixel matching removes some dependence on instrumental resolution does throw away some information encoded in the line shapes

86 ΔCa II [Ca/H] [Ca/H] from the Ca II Triplet W' Bosler, Smecker-Hane, & Stetson 2007 Bosler relation much more believable than Rutledge relation because it's based on Ca no assumption of [Ca/Fe] required 40/46

87 [Fe/H] CaT Metallicities in Leo I [Fe/H]phot 41/46 no correlation between the photometric and MOOG metallicities, but...

88 [Fe/H] CaT First Ever Low-Res [Ca/Fe] [Fe/H]MOOG 42/46 first correlation ever seen between CaT EWs and Fe-line EWs in low res (red) spectra

89 [Ca/H] First Ever Low-Res [Ca/Fe] [Fe/H]MOOG 43/46 these values of [Ca/Fe] are unrealistic however, the correlation, even if slight, is important need to fit CaT with Gaussians to match the way Bosler did it (I used Lorentzians)

90 Things to Work On grid of synthetic spectra to minimize χ2 in {[Fe/H], Teff, log g, ξ} space (i.e., Allende Prieto et al. 2006) better EW measurements need high-resolution stars to compare to M107: 16h33 (visible from Keck II in the west in dusk twilight on Oct 11/12 DEIMOS observing run) 44/46 VALD and Fuhr & Weise Fe line lists are nearly identical to the Kurucz line list I was using M3 is unfortunately a better spring target there are other GCs I could use getting GC data for DEIMOS allows us to put DEIMOS on the R97 scale and allows me to test my method to make sure I get the correct value for the monometallic GC 6 first half-nights total in 2007B means up to 6 twilight GC DEIMOS masks

91 The Future: Coaddition flux rest wavelength (Å) coadd stars of similar photometric properties coadd tens of M31 stars to approximate Leo I spectral quality important to coadd synthetic spectra exactly the same as observed spectra 45/46 I have experience coadding spectra in DEEP2 from the Lyα project

92 Timeline Aug 2007 UMich (Gnedin), The Globular Clusters - Dwarf Galaxies Connection Aug-Sep submit paper with Marla on de radial abundance gradients Sep Sawicki et al. Lyα paper Nov draft of updated low L paper Dec Hayama/Subaru conference (poster) Dec-Feb 2008 Majewski (?) et al. M31 surface brightness profile paper Jan AAS, Austin (poster), visit Chris Jan Leo I abundance paper Feb submit low L paper fall job talks Dec Paper I on abundances in M31 (satellites only?) Jan 2009 AAS, Long Beach (dissertation talk) spring Paper II on abundances in M31 (satellites+halo?) Jun defend thesis 46/46 Jul-Aug get married seven papers planned, five of which are first author getting married is incentive to graduate!