The NGC 2841 GroupThe NGC 2841 Group

February 6, 2007February 6, 2007Tim Dolch, Bridget Falck, Mike SpecianTim Dolch, Bridget Falck, Mike Specian

Huchra & Geller Group MembersHuchra & Geller Group Members

Columns: Name, Velocity, Apparent Magnitude, Morphological Type, Galactic Longitude, Galactic Latitude

H&G MembersH&G Members

NGC 2756NGC 2756 NGC 2681NGC 2681

H&G Member DeterminationH&G Member Determination(Friends of Friends)(Friends of Friends)

1. Choose a galaxy not previously assigned to a group.1. Choose a galaxy not previously assigned to a group.

2. Search for other nearby galaxies within a certain 2. Search for other nearby galaxies within a certain projected radius and within a certain velocity window.projected radius and within a certain velocity window.

3. If no nearby galaxies are found, that galaxy is 3. If no nearby galaxies are found, that galaxy is considered isolated. If other galaxies are found, they are considered isolated. If other galaxies are found, they are added to the group.added to the group.

4. For each galaxy added to the group, repeat step 1.4. For each galaxy added to the group, repeat step 1.

Did H&G Capture Them All?Did H&G Capture Them All?

Probably not…Probably not…

Did H&G Capture Them All?Did H&G Capture Them All?

Did H&G Capture Them All?Did H&G Capture Them All?

Did H&G Capture Them All?Did H&G Capture Them All?

Did H&G Capture Them All?Did H&G Capture Them All?

Did H&G Capture Them All?Did H&G Capture Them All?

What are We Missing?What are We Missing?

What are We Missing?What are We Missing?

Query w/ SDSSQuery w/ SDSS- Many objects with photometry are lacking spectroscopy.Many objects with photometry are lacking spectroscopy.- All photometric objects have photometric redshifts, but these are inaccurate, All photometric objects have photometric redshifts, but these are inaccurate,

especially for these purposes.especially for these purposes.- Sample query:Sample query:

SELECTSELECT s.bestObjID, s.ra, s.dec, s.z as redshift, p.u, p.g, p.r, p.i, p.z s.bestObjID, s.ra, s.dec, s.z as redshift, p.u, p.g, p.r, p.i, p.zFROMFROM SpecObjAll s, PhotoObjAll p, SpecObjAll s, PhotoObjAll p,

fGetNearbyObjEq(140.511,50.97fGetNearbyObjEq(140.511,50.9777,143.25) as N,143.25) as NWHEREWHERE n.objID = s.bestObjID and n.objID = s.bestObjID and n.objID = p.objID andn.objID = p.objID and s.z < 0.00426 ands.z < 0.00426 and s.Objtype = 0 ands.Objtype = 0 and p.type = 3p.type = 3

Query ResultsQuery Results- Using photometric redshifts ~22,000 Using photometric redshifts ~22,000

potential galaxies are returned.potential galaxies are returned.- Using actual redshifts, 22 objects are Using actual redshifts, 22 objects are

returned within 500 kpc.returned within 500 kpc.

Query ResultsQuery Results

Query ResultsQuery Results

Summing Up the Sloan QuerySumming Up the Sloan Query

2841 10.68 r-band mag2841 10.68 r-band mag2756 12.44 r-band mag2756 12.44 r-band mag2681 11.02 r-band mag2681 11.02 r-band magOf the spectroscopic objects found, Of the spectroscopic objects found,

average r-band mag was 16.96average r-band mag was 16.96This amounts to 2 orders mag difference This amounts to 2 orders mag difference

in luminosity, therefore “dwarf” in luminosity, therefore “dwarf” classification not unreasonableclassification not unreasonable

NGC 2841NGC 2841 Sb in Ursa Major, 14.1 Sb in Ursa Major, 14.1

Mpc awayMpc away LINER nucleusLINER nucleus Triaxial bulgeTriaxial bulge Retrograde bulge in outer Retrograde bulge in outer

radiiradii Polar ring orthogoal to Polar ring orthogoal to

galactic planegalactic plane MMdiscdisc = 5 x 10 = 5 x 101010 M Msunsun

VVcc = 317 km s = 317 km s-1-1

M/L ~ 0.7M/L ~ 0.7

L. Portinari, J. Sommer-Larsen, R. Tantalo (2004) MNRAS 347 (3), 691–719.

• NII shows spiral arms (shaded areas)

• Halpha shows elongated loci (contour arms)

• velocity splitting in NII evidence of shock front

ROSAT observations ROSAT observations with halo velocity of with halo velocity of

Infall of gas produces x-Infall of gas produces x-ray bremsstrahlung as ray bremsstrahlung as dominant cooling dominant cooling mechanismmechanism

This gas infall is This gas infall is inconsistent with SFRinconsistent with SFR

An X-Ray View

NGC 2814 in 24 microns from SINGS NGC 2814 in 24 microns from SINGS

Dust not in spatial Dust not in spatial proximity to stars, proximity to stars, so smooth so smooth distribution of dust distribution of dust emission expectedemission expected

2.1 micron 2.1 micron observations show observations show dust emission up dust emission up to 500 pc above to 500 pc above planeplane

A. J. Benson, R. G. Bower, C. S. Frenk, S. D. M. White (2000) MNRAS 314 (3), 557–565.

Unanswered Questions on NGC Unanswered Questions on NGC 2841 Itself2841 Itself

Merger history - Afanasiev et al. speculate that Merger history - Afanasiev et al. speculate that mergers may be necessary to explain dynamical mergers may be necessary to explain dynamical montage - not done to datemontage - not done to date

GALEX data (not yet released) - NGC 2841 is GALEX data (not yet released) - NGC 2841 is “remarkable”“remarkable”

Why is the X-ray emission (LWhy is the X-ray emission (Lx x ~ 10~ 1041 41 erg serg s-1-1) too ) too small (theory => 8 times this) to account for small (theory => 8 times this) to account for accreted SF history? Perhaps could have accreted SF history? Perhaps could have formed surprsingly early - similar examples at formed surprsingly early - similar examples at high z?high z?

NGC 2681NGC 2681

Properties:Properties: Bulge-dominated S0/a galaxyBulge-dominated S0/a galaxy Two concentric, misaligned Two concentric, misaligned

bars and third inner barbars and third inner bar Nucleus is a LINERNucleus is a LINER

Underwent starburst ~1Gyr Underwent starburst ~1Gyr ago?ago?

Hosts a supermassive BH?Hosts a supermassive BH?

Ref: Cappellari, M. et al. 2001, Ref: Cappellari, M. et al. 2001, ApJ, 551, 197ApJ, 551, 197

Recent StarburstRecent Starburst

Strong Balmer absorption lines indicative of Strong Balmer absorption lines indicative of relatively young (1-2 Gyr) stellar componentrelatively young (1-2 Gyr) stellar component

Consistent with relative absorption-line strengths of Consistent with relative absorption-line strengths of Mg II and Mg I, which are indicative of late A-type Mg II and Mg I, which are indicative of late A-type main sequencemain sequence

Stellar M/L for central population is 0.7-1, Stellar M/L for central population is 0.7-1, appropriate for 1-2 Gyr old solar metallicity appropriate for 1-2 Gyr old solar metallicity stellar populationstellar population

Central Black HoleCentral Black Hole Dynamics difficult, but…Dynamics difficult, but…

Kinematics require Kinematics require presence of central BHpresence of central BH

only provides upper limit on only provides upper limit on the mass:the mass:

MMBHBH < 6 x 10 < 6 x 1077 M MSunSun

LINER property suggests LINER property suggests a slow, steady feeding of a slow, steady feeding of a central BHa central BH

Two stellar and two gas Two stellar and two gas velocity dispersions, and velocity dispersions, and model with (solid) and model with (solid) and without (dashed) without (dashed) assumption of central BHassumption of central BH

Evidence for InteractionsEvidence for Interactions

Both presence of supermassive BH and Both presence of supermassive BH and evidence for recent starburst support hypothesis evidence for recent starburst support hypothesis of recent interactions with a neighbor…of recent interactions with a neighbor…

However, no clear signatures of recent accretion However, no clear signatures of recent accretion of gas-rich dwarf, such as morphological of gas-rich dwarf, such as morphological distortions or duplicity of the nucleusdistortions or duplicity of the nucleus

Still open questions about group interactionsStill open questions about group interactions

Future PossibilitiesFuture Possibilities

Measurements of stellar kinematics using Measurements of stellar kinematics using long slit STIS spectra will remove long slit STIS spectra will remove modeling degeneracy, allow pinpointing of modeling degeneracy, allow pinpointing of BH massBH mass

H I survey would shed light on whether H I survey would shed light on whether NGC 2681 underwent a tidal interaction NGC 2681 underwent a tidal interaction with another galaxywith another galaxy

Type Ia Supernova 1999byType Ia Supernova 1999by

Observed in NGC Observed in NGC 28412841

Type Ia SNe are Type Ia SNe are useful as distance useful as distance indicatorsindicators

One of the least One of the least luminous type Ia luminous type Ia events, belonging to a events, belonging to a group of “peculiar” group of “peculiar” subluminous SNe Iasubluminous SNe Ia

Why special?Why special? Host has minimal dust extinction and a Cepheid Host has minimal dust extinction and a Cepheid

distance has been obtaineddistance has been obtained

Allows independent estimate of Hubble Allows independent estimate of Hubble parameter using “peculiar” SNe, since most SNe parameter using “peculiar” SNe, since most SNe calibrated with Cepheids are of “normal” typecalibrated with Cepheids are of “normal” type

Found to be consistent, suggesting no Found to be consistent, suggesting no systematic error due to selection bias of systematic error due to selection bias of calibrated SNecalibrated SNe

Ref: Garnavich et al. 2004, ApJ, 613, 1120Ref: Garnavich et al. 2004, ApJ, 613, 1120