Structure Formation in Tidal Tails

Structure Formation Structure Formation in Tidal Tailsin Tidal Tails

John E. John E. Hibbard Hibbard NRAO-CVNRAO-CV

Structure Formation in Tidal Tails J. Hibbard, NRAO IAU S217 July 17 2003

A Range of Substructures are found in Tidal Tails

Outstanding Questions:On what scales (if any) are these structures bound?Is this an evolutionary sequence?Are these “Tidal Dwarf Galaxies” (TDGs) robust entities?


The Occurrence of Young Stars within The Occurrence of Young Stars within Tidal Debris has been Noted for Some Tidal Debris has been Noted for Some

TimeTime Young StarsDwarf

Re-Re-discovered discovered in the early in the early 1900’s1900’s


TDG TDG “Rogues “Rogues Gallery”Gallery”

Arp 245: Duc et al. 2000AM 1353-272: Weilbacher et al. 2000Iglesias-Paramo & Vilchez 2001NGC3860: Sakai et al. 2002“Tadpole”: Tran et al. 2002

See also the following posters:Lopez-Sanchez et al., #275

Osterloo et al., #284Temporin et al., #315Van Driel et al., #324


• But more But more metal richmetal rich

Duc, 1995, PhD Thesis Univ. Paris

Weilbacher et al. 2003

Properties Properties similar to similar to other other dwarfs…dwarfs…


Formation of Self-gravitating Condensations Formation of Self-gravitating Condensations within Tidal Debris supported by Theoretical within Tidal Debris supported by Theoretical

WorkWork

• Barnes & Hernquist, 1992, Barnes & Hernquist, 1992,

Nature: Swing amplification Nature: Swing amplification

of statistical noise due to N-of statistical noise due to N-

body nature of simulationbody nature of simulation

• Postulate that real disks Postulate that real disks

might have similar “noise” might have similar “noise”

(star clusters, GMCs)(star clusters, GMCs)

• Clumps form primarily from Clumps form primarily from

disk material. Very little dark disk material. Very little dark

mattermatter

• Largest clumps can be gas Largest clumps can be gas

rich, but smallest are gas rich, but smallest are gas

poor (Tpoor (Tgasgas~10~1044 K) K) Barnes & Hernquist, 1992, Nature, 360, 715Barnes & Hernquist, 1992, Nature, 360, 715


From Mihos, 2001, ApJ, 550, 94


WorkWork


From Barnes, 2003, in preparation


WorkWork

• Increased Jeans mass in Increased Jeans mass in tidally agitated disktidally agitated disk

• Dispersion increased, so Dispersion increased, so internal energy is internal energy is increased, requiring increased, requiring larger mass to bind itlarger mass to bind it

• However: Jeans mass is However: Jeans mass is minimum mass that minimum mass that may collapse; doesn’t may collapse; doesn’t say that there will be say that there will be mass condensations mass condensations that large. that large.

Elmegreen, Kaufman & Thomasson, 1993, ApJ:


It is common to call any enhancement a TDG or TDG

candidate. The presumption is that this represents an evolutionary sequence

Form… Grow… Ejected…


Questions to be Questions to be addressed:addressed:

• Are there bound gaseous precursors Are there bound gaseous precursors to optical condensations?to optical condensations?

• Are TDGs bound by baryons alone?Are TDGs bound by baryons alone?• Can the physical properties of tidal Can the physical properties of tidal

substructures be accurately derived?substructures be accurately derived?• Do Super Star Clusters (SSC) occur Do Super Star Clusters (SSC) occur

within tidal tails?within tidal tails?


Under many TDG evolutionary scenarios, Under many TDG evolutionary scenarios, optical TDGs should have gaseous optical TDGs should have gaseous

precursorsprecursors

• Use distribution and Use distribution and kinematics of kinematics of moderate resolution moderate resolution HI observations to HI observations to estimate dynamical estimate dynamical nature of gaseous nature of gaseous substructure substructure

VLA observations of NGC 4038/9: Hibbard, Barnes, van

der Hulst & Rich, 2001


Identified clumps in tails with contrast of 2 from Identified clumps in tails with contrast of 2 from surrounding material, and with S/N>6surrounding material, and with S/N>6

Also Identified an equal number of "interclump" Also Identified an equal number of "interclump" regionsregions


MM**/L/LBB=5 =5 exp SFH, 10 Gyrexp SFH, 10 Gyr

• 2T = -U2T = -U33

2 2 = G M = G Mvir vir /(aR/(aR1/21/2) )

MMvirvir = 1.91x10 = 1.91x1066 2 2 RR1/21/2

• MMgasgas=1.36M=1.36MHIHI

• MMstarsstars=(M=(M**/L/LBB) * L) * LBB

• filled symbols = filled symbols = foreground & foreground & background background subtractionsubtraction

MM**/L/LBB=0 =0

MM**/L/LBB=2 =2

const SFH, 10 Gyrconst SFH, 10 Gyr

Dynamical Analysis: Is there enough Dynamical Analysis: Is there enough mass in gas and stars to make mass in gas and stars to make

clumps bound? clumps bound?


NGC 7252, NGC 3921: Concentration of gas, young stars, HII regions coincide with increased HI velocity width.

If bound, then M/L~4-6; Mvir/Mbaryons~2

Hibbard et al. 1994, Hibbard & van Gorkom 1996

See also: Temporin et al. 2003 (poster #315)Mendes de Oliveira et al. 2001(M/L~5-17)Expect M/L<2 for disk(especially in light of observed HII regions)


For reasonable MFor reasonable M**/L, clumps and TDG candidates /L, clumps and TDG candidates require significant dark matter to be self-require significant dark matter to be self-

gravitatinggravitating

Red points from Braine et al. 2001, A&A, 378, 51Blue points from Hibbard et al., in preparationX’s = clumps in S. tail of NGC 4038

Baryon dominated

Dark Matter dominated

Log Log (

Log

(

)

)

• The condensations The condensations they point to are they point to are very dark matter very dark matter dominated dominated

Mjeans Mjeans/MHI

(Mo)

2.8E10 361.2E10 12

6E09 116E09 156E09 165E09 114E08 23E10 212E10 84E09 40

Elmegreen, Kaufman & Thomasson, 1993, ApJ:


Recent Observations show drastic Recent Observations show drastic kinematical gradients across kinematical gradients across

candidatescandidates

• Optical emission lines (HOptical emission lines (H, H, H, [OIII]), [OIII])• Gradients of 100’s km/s across 1-2 kpcGradients of 100’s km/s across 1-2 kpc• Not all appear to be a locations where tail Not all appear to be a locations where tail

is bending back along line-of-sightis bending back along line-of-sight• Inferred dynamical masses up to 10Inferred dynamical masses up to 101010 M Moo

• Implies M/LImplies M/LBB ~ 100-200 M ~ 100-200 Moo/L/Loo

See also: Temporin et al, Poster #315; Lopez-Sanchez et al. Poster #275


Weilbacher, Duc, Fritze-v.Alvensleben 2003, A&A[OIII]


““Dentist Dentist Chair” Chair” GalaxyGalaxy

Weilbacher et al. 2002, ApJ

Velocities from H


High resolution N-body model of “The High resolution N-body model of “The Mice”Mice”

• Bulge-disk-Halo Bulge-disk-Halo progenitors (Barnes progenitors (Barnes (1988, 1996)(1988, 1996)

• MMdarkdark/M/Mlumlum=4=4

• 1E6 particles1E6 particles– 64k per bulge64k per bulge– 200k per disk200k per disk– 300k per halo300k per halo

Barnes & Hibbard, in preparation


Fit HI, CO, Halpha morphology Fit HI, CO, Halpha morphology and kinematicsand kinematics

HI: Hibbard & van Gorkom 1996; CO: Yun & Hibbard 2001; Halpha: Mihos et al. 1993


High resolution allows High resolution allows significant number of significant number of

particles per TDGparticles per TDG

• NNmaxmax ~ 1100 ~ 1100

• Allows accurate Allows accurate determination of determination of physical physical properties (half-properties (half-light radius, light radius, velocity velocity dispersion, virial dispersion, virial mass)mass)


Identify 64 clumps at late times Identify 64 clumps at late times (~300 Myr from today) with E/m<0, (~300 Myr from today) with E/m<0,

T/U<-0.5T/U<-0.5

• Restrict this to 18 with N>50, well defined peakRestrict this to 18 with N>50, well defined peak• Particles extracted from tail & measure half-Particles extracted from tail & measure half-

light radius and velocity dispersionlight radius and velocity dispersion• Physical scales set by match to observationsPhysical scales set by match to observations


Do bound regions show distinct Do bound regions show distinct observational signatures?observational signatures?

• Sometimes…Sometimes…– Most clumps correspond Most clumps correspond

to density enhancementsto density enhancements– Larger clumps visible Larger clumps visible

have enhanced velocity have enhanced velocity dispersiondispersion

• But…But…– Not all clumps are Not all clumps are

obvious enhancementsobvious enhancements– Not all enhancements Not all enhancements

are bound clumpsare bound clumps– Most clumps have Most clumps have

dispersion ~ interclump dispersion ~ interclump material, so are not material, so are not distinctdistinct

– Projection effects can Projection effects can wipe out signatureswipe out signatures

Face-on

Inclined


Face-on

Inclined


Ability to Ability to recover recover true true physical physical parameters parameters depends on depends on resolutionresolution……


……and, and, most most importantlimportantly, on y, on viewing viewing angleangle


Ability to derive true properties Ability to derive true properties depends critically on viewing depends critically on viewing

angleangle

Face-on Inclined

Mtotal=5E9 Mo


VLA B-array HI Mapping of NGC 4038/9FWHM = 4.5”x4.0” = 415x370pcTspin = 120 KNHI,peak = 3x1021 cm-

2

MHI = 1x107 Mo

HIHI = 5 km/s

Rhalf = 500 pcMvir = 3x107 Mo

Some regions may be bound, but on smaller scales

Compare C+D Array:Tspin = 40 KNHI,peak = 1.4x1021 cm-2

MHI = 2.4x108 Mo

HI HI = 13 km/s

Rhalf = 3.2 kpc Mvir = 1x109 Mo

Hibbard & Higdon, in preparation


Tidal Substructure Tidal Substructure Conclusions:Conclusions:

• Most condensations do Most condensations do not have enough not have enough luminous matter to be luminous matter to be self-gravitating. self-gravitating.

• If they ARE self-If they ARE self-gravitating, they must gravitating, they must be dark matter be dark matter dominateddominated

• Recent kinematical Recent kinematical signatures very signatures very intriguing – require intriguing – require large amounts of dark large amounts of dark matter matter

• Derivation of dynamical Derivation of dynamical properties confused by properties confused by adjacent tidal material, adjacent tidal material, resolution, and resolution, and especially projection especially projection effects effects

• Many TDG candidates Many TDG candidates may be collection of may be collection of smaller bound units. In smaller bound units. In this case, mass scale this case, mass scale may be more may be more appropriate to dSph than appropriate to dSph than to dIrr to dIrr



• Would be very reassuring to find Would be very reassuring to find evidence of kinematically distinct TDG evidence of kinematically distinct TDG candidate in face-on systemcandidate in face-on system

Arp 107


HST study of Optical Substructure in Tidal Tails

N4038/9, N3256 N3921, N7252WFC VI13 orbitsP.I. Charlton Kniermann et al. AJ, submitted

N4038 TDG WFC UBVI11 orbitsP.I. Hibbard Saviane et al. AJ, submitted

After correcting for background After correcting for background contamination, only one tail shows contamination, only one tail shows

significant population of compact sources significant population of compact sources

Knierman et al., AJ, submitted

NGC 4038 S

NGC 3256 W

Despite the lack of a significant tidal population of star Despite the lack of a significant tidal population of star clusters, there are concentrations of star clusters clusters, there are concentrations of star clusters

associated with the TDG candidates in both NGC 7252 associated with the TDG candidates in both NGC 7252 and NGC 4038and NGC 4038


No similar No similar population in population in CMD either CMD either on or off the on or off the tailtail


NGC 4038 TDG Candidate. NGC 4038 TDG Candidate.

HST: Saviane, Hibbard & Rich, AJ, submittedHI: Hibbard, van der Hulst, Barnes & Rich, 2001

N

E

HST WFPC2 Truecolor (V,V+I,I) HST WFPC2 Truecolor (V,V+I,I) with HI contourswith HI contours

Star Cluster concentration in TDG Star Cluster concentration in TDG Candidate in the S tail of NGC 4038Candidate in the S tail of NGC 4038

Location of Tail Star ClustersSaviane, Hibbard & Rich, AJ, submitted

Tail star clusters compared to SSCs in inner regions: smaller,

more irregular



• Bright star clusters Bright star clusters sometimes, but not sometimes, but not always, found in tailsalways, found in tails

• Star clusters “often” Star clusters “often” concentrated in vicinity concentrated in vicinity of TDG candidatesof TDG candidates


Fate of Fate of clumps?clumps?

• Most tidal material remains Most tidal material remains

bound to remnant, streams bound to remnant, streams

back in on scales of Gyr back in on scales of Gyr

• Bound units will be tidally Bound units will be tidally

heated and stripped down to a heated and stripped down to a

few % of original massfew % of original mass

• In cluster environment, outer In cluster environment, outer

regions will be strippedregions will be stripped

• Fate of more energetic ends of Fate of more energetic ends of

tails depends on dark matter tails depends on dark matter

contentcontent

Barnes & Hernquist, 1992, Nature, 360, 715Barnes & Hernquist, 1992, Nature, 360, 715

Structure Formation in Tidal Tails

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