1. The M-81 Group of Galaxies Brian Fleming Stephanie LaMassa Seamus Riley (The Chunky Ponies)

2. Outline Overview Overview Makeup of M81 – Major Members & Structure Makeup of M81 – Major Members & Structure Kinematics of the group Kinematics of the group Interactions Interactions

3. The M-81 Group One of the nearest to the LG One of the nearest to the LG Similar Morphology and Binary Structure Similar Morphology and Binary Structure Bordered on either side by bright galaxies NGC 2403 and NGC 4236 Bordered on either side by bright galaxies NGC 2403 and NGC 4236 Between LG and M81 is 3MPc of nothing <-9mag Between LG and M81 is 3MPc of nothing <-9mag Until 1998 only the distances to M81 and NGC 2403 were known via Cephids – limited research, kinematcs Until 1998 only the distances to M81 and NGC 2403 were known via Cephids – limited research, kinematcs Angular Radius ~ 8 degrees Angular Radius ~ 8 degrees Dominated by M81 Galaxy – similar to MW or M31 Dominated by M81 Galaxy – similar to MW or M31 M B =-20.47 M B =-20.47 V rot =250km/s V rot =250km/s R~500 kpc R~500 kpc 25 probable companions known 25 probable companions known

4. M81 in Galactic Coordinates M-81 Cluster flanked by NGC 2403 and NGC 4236 Filament has angular size ~ 25 o

5. Central M81 25 known satellites of M81 Sample biased towards brightness and location 11 Sph 12 Irr (M82, NGC 3077) 1 Sb (M81) 2 Sm (NGC 2574, NGC 2976) At least 44 GC Missing mass suggests many more undiscovered Dwarves & GC

6. Properties of M81 Karachentsev et al. 2001 – The M81 Group of Galaxies: New Distances, Kinematics, and Structure Karachentsev et al. 2001 – The M81 Group of Galaxies: New Distances, Kinematics, and Structure Using HST WFPC2 and Tip of the Red- Giant Branch method, determined distances to 13 of the late type galaxies around M81 Using HST WFPC2 and Tip of the Red- Giant Branch method, determined distances to 13 of the late type galaxies around M81 15 CMD (V-I) with anywhere from 1,000 to 20,000 stars per image 15 CMD (V-I) with anywhere from 1,000 to 20,000 stars per image Distances and Radial Velocities allow determination of cluster mass and study of 3-D structure and kinematics Distances and Radial Velocities allow determination of cluster mass and study of 3-D structure and kinematics

7. TRGB for M82 Sakai & Madore 1999 Method effective for most objects in M81 since we can still resolve stars in the halo Age and Metalicity independent Slight reddening by dust

8. Mass Estimates Karachentsev et al. 2001: 16 of the M81 objects have measured radial velocities, so a mass estimate is possible: Karachentsev et al. 2001: 16 of the M81 objects have measured radial velocities, so a mass estimate is possible: Virial Mass Estimate: Virial Mass Estimate: N=# of objects, σ 2 =dispersion of radial velocities w/respect to group centroid (σ v =84km/s), and R H =Harmonic radius of the group (57kpc) N=# of objects, σ 2 =dispersion of radial velocities w/respect to group centroid (σ v =84km/s), and R H =Harmonic radius of the group (57kpc) M vir (M81)=0.94x10 12 M๏ M vir (M81)=0.94x10 12 M๏ NGC 2403 with 4 DIrr and 1 DSph have M vir (NGC 2403)=0.26x10 12 M๏ NGC 2403 with 4 DIrr and 1 DSph have M vir (NGC 2403)=0.26x10 12 M๏ Groups with dominant central galaxies can use orbital motion: Groups with dominant central galaxies can use orbital motion: M ORB (M81)=1.63x10 12 M๏ M ORB (M81)=1.63x10 12 M๏ M LG =1.29x10 12 M๏ M LG =1.29x10 12 M๏

9. Globular Cluster Properties Schroder et al. – Spectra of 44 M-81 GC using Keck I, 2002 Schroder et al. – Spectra of 44 M-81 GC using Keck I, 2002 Similar to MW GC: Similar to MW GC: No bimodality detected yet No bimodality detected yet

10. Kinematics: Filament structure: does not fit free expansion models NCG 2403: approaching M81 NGC 4236: moves away from M81

11. Relative Velocities Velocities relative to M81 demonstrate: Cosmological expansion at distances R > 1 Mpc (No galaxies approaching M81) Galaxies only approaching M81 for 1>R>.55 Mpc (infall zone) Objects moving both towards and away for R<.55Mpc (“Virialized” Zone) Zero Velocity surface is R 0 = (1.05 ±0.07) Mpc

12. Arp Paradox (1982) The number of M81 Companions with positive and negative peculiar velocities has a ratio of 13:3 The number of M81 Companions with positive and negative peculiar velocities has a ratio of 13:3 Suggested that selection occurs when “HI line emission of galaxies with V h < 0 km/s is blended with strong Galactic emission” (Karachentsev et al 2002) Suggested that selection occurs when “HI line emission of galaxies with V h < 0 km/s is blended with strong Galactic emission” (Karachentsev et al 2002) -this would imply many missing galaxies -this would imply many missing galaxies Could also be explained by peculiar velocity of M81 (~50 km/s) with respect to group center of mass Could also be explained by peculiar velocity of M81 (~50 km/s) with respect to group center of mass

13. Hot Gas on Outskirts of M81 (2003) Bureau at el. examined HoII using the VLA to determine nature of HI morphology Could be the result of tidal interactions with the low mass M81dwA M81dwA may be a tidal dwarf of HoII, formed by the gravitational collapse of tidal debris from interactions with a third galaxy, UGC 4483 Tails could be a result of ram pressure stripping through an IGM encounter Search for stellar counterpart to HI in arms would resolve issue

14. HI in the M81 Group Distribution of gas between galaxies is affected by tidal interactions Distribution of gas between galaxies is affected by tidal interactions Yun et al. (1994) mapped the H1 distribution in the M81 group using the VLA Yun et al. (1994) mapped the H1 distribution in the M81 group using the VLA M81 M82 NGC3077 Integrated H1 Map Palomar sky survey “south tidal bridge” “north tidal bridge”

15. HI in the M81 Group (cont.) Results of Yun et al.'s study: Results of Yun et al.'s study: filamentary structures seen in HI image indicate tidal interactions have disrupted this system filamentary structures seen in HI image indicate tidal interactions have disrupted this system M81 M81 HI spiral arms trace the optical arms HI spiral arms trace the optical arms HI spiral arms beyond the optical disk HI spiral arms beyond the optical disk M82 M82 H1 streamers > 30 kpc emerging from stellar disk; evidence for tidal disruption of outer H1 disk by massive companion H1 streamers > 30 kpc emerging from stellar disk; evidence for tidal disruption of outer H1 disk by massive companion

16. HI in the M81 Group (cont.) Boyce et al. (2001) used the HI Jodrell All-Sky Survey (HIJASS) to survey HI in the M81 Group Boyce et al. (2001) used the HI Jodrell All-Sky Survey (HIJASS) to survey HI in the M81 Group ● two dIrr galaxies (Holmberg IX and A952+69) are within the tidal bridge between M81 and M82 ● They suggest these galaxies are “tidal dwarf galaxies,” formed from the tidal debris between M81 and M82 ● dIrr galaxy Garland is in the tidal tail between M82 and NGC 3077 and may also be a tidal dwarf galaxy.

17. H1 in the M81 Group (cont.) Study of stellar distributions within the H1 regions undertaken by Sun et al. (2005) using Beijing-Arizona-Taipei-Connecticut (BATC) survey Study of stellar distributions within the H1 regions undertaken by Sun et al. (2005) using Beijing-Arizona-Taipei-Connecticut (BATC) survey ● Image from survey with the Yun et al. (1994) H1 map overlaid ● Region contains M82, most of M81 and half of the north tidal bridge

18. HI in the M81 Group (cont.) Results from survey Results from survey coexistence of stellar and HI components in the intergalactic region coexistence of stellar and HI components in the intergalactic region stars are probably tidal in origin stars are probably tidal in origin further evidence of disruption of M82 disk from M81 and M82 passing by each other further evidence of disruption of M82 disk from M81 and M82 passing by each other

19. Bibliography Arp, H. 1982, ApJ, 256, 54 Bureau, M., Walter, F., van Gorkom, J., Carignan, C. International Astronomical Union Symposium no. 217, held 14-17 July, 2003 in Sydney, Australia. Edited by P.-A. Duc, J. Braine, and E. Brinks. San Francisco: Astronomical Society of the Pacific, 2004., p.452 Karachentsev, I. D., et al. 2002a, A&A, 383, 125 Schroder et al. – Spectra of 44 M-81 GC using Keck I, 2002