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Поисковые слова: arp 220
Bulges and disks in spiral galaxies: Clues for secular evolution?

Leslie Hunt INAFIstituto di Radioastronomia, Sezione Firenze

Tracing Dust in Spiral Galaxies Ghent 1317 May 2007


Galaxy Hubble types

N2775 (SAab) [Frei] N1350 (SBab) [OSU]

M51 (SAbc) [NOAO] M100 (SABbc) [Frei] Tracing Dust in Spiral Galaxies Ghent 1317 May 2007


Main structural components: bulge and disk

Bulge = spheroidal component, kinematically ~pressure supported with Vrot/* small ("hot")
Light distribution modeled by generalized exponential (Sersic), oblate ellipsoid coplanar with disk

Ie, re = effective (halflight) values B = apparent bulge ellipticity n = scaling constant relating effective to exponential values

Disk = approximately flat component, kinematically rotationally supported with Vrot/* large ("cool")
Modeled by simple exponential (Freeman 1970)
Tracing Dust in Spiral Galaxies Ghent 1317 May 2007


Spiral galaxies in context

Elliptical

M 100

M 51

N 6090

M 82

Arp 220
Tracing Dust in Spiral Galaxies Ghent 1317 May 2007

SEDs (GRASIL, Silva et al. 1998) with different dust opacities


Effects of dust: NGC 4826 (Black or evileye galaxy)
GarciaBurillo et al. 2003 (NUGA) IRAC 3.6 m (SINGS) H I B HST (Heritage)

Tracing Dust in Spiral Galaxies Ghent 1317 May 2007


Twodimensional bulge/disk decompositions at ~2 m
Why 2D?
Mandatory for non faceon objects. Better able to suppress nonaxisymmetric structure (e.g., "folding" about minor, major axes) such as bars, twisted isophotes, spiral arms.

Why use > 1.6 m?
To mitigate effects of dust (AH, AK 79 times lower than AV) which could skew structural parameters including surface brightnesses and scalelengths (Beckman et al. 1996; Pompei & Natali 1997; Mollenhoff et al. 2006). To more directly trace mass (Rix & Rieke 1993; Gavazzi 1993) and be less sensitive to recent starformation episodes which dominate disk morphology at optical wavelengths.
e.g., de Jong 1996 + Graham 2001, 1D (86 galaxies); Moriondo et al. 1998
(14); Khosroshahi et al. 2000 (26); Mollenhoff & Heidt 2001 (40); MacArthur et al. 2003 (28); Hunt, Pierini, & Giovanardi 2004 (122); Grosbol et al. 2004 (54)
Tracing Dust in Spiral Galaxies Ghent 1317 May 2007


N value for bulge drastically changes the light profile...

n=4

Higher n bulges more centrally peaked and more extended curvature at large radii than smallern bulges.

n=4
Sersic profiles for different n. Top panel effective surface brightness e constant; bottom panel central surface brightness 0 constant. (Taken from MacArthur et al. 2003.)
Tracing Dust in Spiral Galaxies Ghent 1317 May 2007


Bestfit n value has a strong influence on derived B/D ratios (larger with increasing n)

Total magnitude

Surface brightness

Log (scalelength)

n
(Taken from Moriondo et al. 1998)

n

Tracing Dust in Spiral Galaxies Ghent 1317 May 2007


How to determine best n?

We discretize n and run separate models (don't forget seeing convolution). Then use radial run of 2 for different values of n (1, 2, 3, 4) to decide on best fitting value.

Best n=4

n=14 covers the range observed in 90 95% of spirals range from S0/a to Scd. Other groups fit n but since Ie, re, not independent of n, such bulge+disk decompositions are more uncertain. In any case, uncertainty n ~= 1
Best n=1
Tracing Dust in Spiral Galaxies Ghent 1317 May 2007


Bulge shape and Hubble type
Earlytype bulges have higher n number (more centrally cusped and extended) than latetypes.
Andredakis et al. 1995

Hunt et al. 2004

Mollenhoff & Heidt 2001

Tracing Dust in Spiral Galaxies Ghent 1317 May 2007


Trends with bulge shape n

Report effective values because otherwise fitting function defines trends. Largen bulges are more extended (larger re) and more luminous (brighter M). Disk parameters remain relatively constant with bulge shape.

Tracing Dust in Spiral Galaxies Ghent 1317 May 2007


Trends with Hubble type

Latetype spirals have more tenuous (larger e) and less luminous bulges (fainter M) (c.f. Mollenhoff & Heidt 2001).

Disk parameters remain relatively constant with Hubble type, although late types may have more tenous (larger e) disks.

Tracing Dust in Spiral Galaxies Ghent 1317 May 2007


The "iceberg scenario" and the "scalefree" Hubble sequence

Graham (2001): iceberg scenario B/D luminosity ratios much greater for earlytype spirals (partially obvious because of classification criterion). But NOT from re/rd, but rather because of the iceberg and bulge shape n (Graham 2001; Hunt et al. 2004). Scale free: re/rd invariant with T (Courteau et al. 1996; MacArthur et al. 2003).
Tracing Dust in Spiral Galaxies Ghent 1317 May 2007


Scalefree: more fundamental bulge shape n or Hubble type?

Bulge and disk parameters tightly correlated for n=1 bulges, but correlations worsen with n so that by n=4 bulges are Traci virtually independent of disks.

ng Dust in Spiral Galaxies Ghent 1317 May 2007


red bulges

blue bulges

Driver et al. 2006 Millenium GS

Tightness of Kormendy relation for bulges
(projection of Fundamental Plane, FP) depends on their shape parameter n: e and log(re) tightly correlated for n=4 (more virialized or structurally defined?) but only very weak correlation at n=1.
Tracing Dust in Spiral Galaxies Ghent 1317 May 2007


Formation and evolutionary scenarios for spiral galaxies
Bulges form before disks:

versus

Bulges form from disks through secular evolution: Bar thickening or destruction (Kormendy 1979; Combes & Sanders 1981; Combes et al. 1990; Pfenniger & Norman 1990; Friedli & Benz 1995; Martinet 1995; Norman et al. 1996; Kormendy & Kennicutt 2004), amplified by gas dissipation (Junqueira & Combes 1996), forms a central concentrated vertically heated structure ~"bulge" Collective dissipation processes linked to spiral density waves (Zhang 1996, 1998, 1999)
Tracing Dust in Spiral Galaxies Ghent 1317 May 2007

"Monolithic collapse" (e.g., Eggen et al. 1962) or infall of enriched gas from the star forming halo (Carney et al. 1990) Merging of stellar disks within their (merging) CDM halos (Kauffmann et al. 1993; Baugh et al. 1996; ...) Merging of dense satellites (Aguerri et al. 2001)


Formation and evolutionary scenarios for spiral galaxies, continued...

"versus" or variation
Initial conditions are everything: "Insideout" scheme of van den Bosch (1997) in which collapsing halo forms unstable disk (e.g., Fall & Efstathiou 1980), part of which rapidly becomes a "bulge", the remainder settling into a disk

Taken from Bothun (2000) Tracing Dust in Spiral Galaxies Ghent 1317 May 2007


The impact of bulge/disk scaling relations on spiral galaxy formation and evolution
Close relation between exponential bulges and their disks CONFLICT with "monolithic collapse" or CDM merging. If initial conditions dominate, then bulges and disks should be unrelated! Maybe true for high n bulges, but CONFLICT with gradual worsening of bulge/disk correlations with n. Low B/D ratios CONFLICT with "insideout" scheme of van den Bosch (1997) because unstable disks would be expected to always form some bulge. Also disks and bars may not always be shortlived (e.g., Athanassoula & Misiriotis 2002; Valenzuela & Klypin 2003; Shen & Sellwood 2004; Debattista et al. 2006). More natural explanation of scaling relations is secular evolution in which n=1 bulges are relatively young, having formed recently from their disks (either dissipatively or not, but see Regan et al. (2006) who find more ISM in n=1 bulges than in higher n.) Angular momentum spread in a given galaxy reflects how long secular processes have been at work.

Taken from Kannappen 2003 Tracing Dust in Spiral Galaxies Ghent 1317 May 2007


The Hubble Sequence: nature or nurture? Or a sequence in bulge shape?
Hypothesize that exponential n=1 bulges younger than highern ones, independently of T.

Supported by blue VH colors (Carollo et al. 2001), and good correlation of bulge/disk structural, kinematic, chemical properties of latetype bulges (Wyse et al. 1997; Carollo 2004; Kormendy & Kennicutt 2004). increases as T decreases but independent of n: higher stellar surface densities in early Hubble types imply more evolved systems (prolonged SF). If bulge n increases with time (as in Zhang models), re and M(bulge) also. T and n correlated implies both reflect evolutionary state?
Tracing Dust in Spiral Galaxies Ghent 1317 May 2007


What about bars?
Frequently occurring, putative driver of secular evolution! But models appear unable to produce n=4 bulges. However, kinematics of barlike pseudobulges successfully reproduced (e.g., Bureau et al. 2006). Mergers (fast) in the past and (slow) secular evolution in future?

BOTTOM LINE: SPIRAL GALAXIES OBEY WELL DEFINED SCALING RELATIONS which need to be taken into account.
Tracing Dust in Spiral Galaxies Ghent 1317 May 2007


Stellar bars as structural components
Can furnish up to 1/3 of galaxy's total luminosity. Typically composed of old stars (and thus dynamically important). Modify morphology, both because of their APPEARANCE and because of their DYNAMICAL EFFECTS.

Quantify photometric properties of bars (e.g., Elmegreen et al. 1996)
Measure length Rbar and normalize to optical radius Ropt . Measure brightness profile along major axis and minor axis.

Using galaxies with welldefined RC3 bar classes
(SA, SAB, SB) in the PiscesPerseus sample imaged in H band (Moriondo et al. 1999 = 110 galaxies of 174 total).
Tracing Dust in Spiral Galaxies Ghent 1317 May 2007


BAR major axis brightness profiles come in two "flavors": exponential flat

N925 (SABd)

N1300 (SBbc) [HST Legacy]

Tracing Dust in Spiral Galaxies Ghent 1317 May 2007


Bars in earlytype spirals tend to be FLAT and LONGER than those in latetypes which tend to have SHORTER and EXPONENTIAL bars
When normalized (to Ropt) bar lengths Rbar plotted against T, trend for Rbar /Ropt to decrease with increasing Hubble type. Mainly true because FLAT BARS longer than EXPONENTIAL ONES. (Elmegreen et al. 1996; Hunt & Giovanardi 2007, in preparation)

X exponential bars Tracing Dust in Spiral Galaxies O flat bars Ghent 1317 May 2007


Hypothesize (speculate?) that EXPONENTIAL bars are younger than FLAT bars, independently of T.
Bars get LONGER and STRONGER with time (Combes & Elmegreen 1993; Athanassoula 2002, 2003). Perhaps BARS themselves EVOLVE from exponential to flat types, perhaps promoting the evolution of the Hubble type in which they reside (?) Because of the type dependence of exponential and flat bars on late and early spiral types, all this could happen together with the gradual growth of bulge/disk ratio (either through mergers, accretion, or barmediated inflow)... It is possible that bar morphology and dynamics are intimately related to the Hubble type of a galaxy, being part and parcel of its genesis.

Spiral galaxies are not arbitrary collections of structural components: distinct types of bulges, disks, and bars tend to be associated with Hubble types, and may indirectly (or directly) define them.
MANY THANKS TO THE ORGANIZERS!

Tracing Dust in Spiral Galaxies Ghent 1317 May 2007