Bulk Motions of Spiral Galaxies within z = 0.03 I.D.Karachentsev (SAO RAS ), S.N.Mitronova (SAO RAS), V.E.Karachentseva (Kiev Univ.), Yu.N.Kudrya (Kiev Univ.) The 2MASS View of NGC 891

The RFGC (Karachentsev et al. 1999) includes 4236 galaxies with optical angular diameters a>0.6' and apparent axial ratios a/b>7. The RFGC is currently the most uniform all-sky catalog of edge-on late-type spiral galaxies. Based on optical TF-relation for 971 galaxies we obtained the dipol parameters : V = 300 ± 75 km/s, l = 328 o ± 20 o, b = +7 o ± 15 o.

About 3000 galaxies in RFGC have J,H,K photometry in the 2MASS survey. We constructed the 2MASS-TF relations for a sample of 1141 galaxies and determined the bulk motion parameters: V = 226 ± 62 km/s, l = 295 ± 16 o, b = –2 ± 13 o (Kudrya et al. 2003)

2MASS обзор

Images of the 2MFGC galaxies

The 2MFGC catalog (Mitronova et al. 2004) contains IR photometry and LEDA and NED identifications for galaxies with axial ratios a/b > 3 in the XSC-2MASS

All-sky distribution of MFGC galaxies

The TF relations

The 2MFGC galaxies with known V and W

Magnitude of the bulk velocity (dots) vs depth

The basic relations: M = J – 25 – 5 log r, r = V 3K / H o {1 – (q o - 1)V 3K / 2c}, where q o = for standard ΛCDM. M = C 1 + C 2 log W + C 3 log R eff + C 4 a/b + C 5 (IC), V pec = V 3K – H o r {1+(q o - 1) H o r / 2c}. We use the set of peculiar velocities to calculate the orthogonal components of the dipole bulk velocity V, _ _ V pec,i = V e i + ∆V i by minimizing the sum of the squares of the “noise” peculiar velocity component.

Parameters of the 2MFGC dipole bulk velocity: Excluding galaxies with deviations of more than 3σ(TF) and V pec > 3000 km/s, we obtain: N = 2395 σ(TF) = 0.45 mag, σ(V) = 968 km/s, V = 199± 37 km/s, l = 290 o ± 11 o, b = +1 o ±9 o

Bulk motion in the Local Group frame: The Sun moves relative to the 3K frame with a velocity of V 3K = ± 3.0 km/s towards l = ± 0.3 o, b = ± 0.5 o (Kogut et al. 1993), while the LG centroid has a velocity of V 3K (LG) = 634 ± 12 km/s relative to the 3K frame in the direction l = 269 ± 3 o, b = +28 ± 1 o (Karachentsev & Makarov 1996). In the LG frame the bulk motion is: V 3K = 372 ± 33 km/s in the direction l = 76 ± 6 o, b = -40 ± 6 o. Returning to the 3K frame, we obtain: V = 296 km/s, l = 282 o, b = +11 o.

Sky distribution of 2MFGC galaxies in the shells in Galactic coordinates

Parameters of the dipole bulk velocity for the 2MFGC galaxies in spherical shells Sample, N σTF mag σV km/s V km/s l deg. b deg. F S1, ± ± 6 4 ± 431 S2, ± ± ± S3, ± ± ± 96.4 S4, ± ± ± 181.8

Peculiar velocity distribution for MFGC galaxies in Galactic coordinates

The peculiar velocity field The peculiar velocity distribution of 2MFGC galaxies is asymmetric: the maximum positive isovelocity is +350 km/s, while the maximum negative isovelocity is only 150 km/s. The Vpec appears doubly connected, with the primary peak being approximately in the zone where the Hydra-Centaurus, Norma, A3627 clusters and the Shapley Concentration of clusters are located. The secondary positive peak with an amplitude of 150 km/s is identified with the Abell cluster A400 (170 o, -45 o ) and A539 (196 o, -18 o ). The region of negative mean peculiar velocities forms three broad shallow troughs with the coordinates of their centers (120 o, +40 o ), (80 o, -30 o ), (200 o, +30 o ). The first two of them lie not far from the well- known Void in Bootes and the Local Void.

To estimate the representativeness and quality of the galaxy sample used to determine the dipole parameters, we introduced the concept of goodness, G = (N/100 ) 1/2 /σ(TF), where N is the number of galaxies in the sample, and TF is their dispersion (in magnitudes) in the TF diagram. Goodness for various samples: Sample G V l o b o Reference km/s Spirals in clusters Dale et al. (1999) SNIa Radburn-Smith et al. (2004) RFGC –2 Kudrya et al. (2003) Mark III Dekel et al. (1999) 2MFGC This talk

The sample of 2MFGC galaxies has the best goodness. The parameters of the 2MFGC dipole are in good agreement with their weighted mean values for all five samples: V = 225 ± 47 km/s, l = 295 o ± 3 o, b = +6 o ± 5 o. These amplitude and direction of the bulk motion can be currently taken as the standard ones for the bulk flow of galaxies relative to the CMB on a scale of ~100 Mpc. This direction of the dipole is almost opposite to the direction of the rotational velocity of the Sun relative to the Galactic center, V = 220 km/s, l = 90 o, b = 0 o. For this coincidental reason, the large-scale flow of galaxies had gone unnoticed until the 1980s.

Conclusions The apex of the bulk flow is located roughly in the same region as the all-sky X-ray selected cluster dipole: l = 292 o, b = +3 o (Kocevsky & Ebeling 2005). If judged by the pattern of decrease in the flow amplitude with linear scale of the Local Volume, then objects (attractors) located farther than 50 Mpc could be responsible for ~60% of the amplitude of the observed bulk motion of 2MFGC galaxies.

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