Jet-Disturbed Molecular GasJet-Disturbed Molecular Gas Near the Seyfert 2 Nucleus in M51 Near the Seyfert 2 Nucleus in M51

Satoki Matsushita, Sebastien Muller, & Jeremy LimSatoki Matsushita, Sebastien Muller, & Jeremy Lim

AbstractAbstract We carried out CO(2-1) & CO(1-0) line observations of the nuclear region of Seyfert 2 galaxy M51 with the new A confiWe carried out CO(2-1) & CO(1-0) line observations of the nuclear region of Seyfert 2 galaxy M51 with the new A configuration of the IRAM Plateau de Bure Interferometer (PdBI), yielding a spatial resolution lower than 15 pc. The images guration of the IRAM Plateau de Bure Interferometer (PdBI), yielding a spatial resolution lower than 15 pc. The images show no clear evidence of the previously suggested putative circumnuclear disk around the nucleus, but show two sepashow no clear evidence of the previously suggested putative circumnuclear disk around the nucleus, but show two separate features located on the eastern and western sides of the nucleus. The western feature shows an elongated structurate features located on the eastern and western sides of the nucleus. The western feature shows an elongated structure along the radio jet and a good velocity correspondence with optical emission lines associated with the jet, suggesting re along the radio jet and a good velocity correspondence with optical emission lines associated with the jet, suggesting that this feature is a jet-entrained gas. The eastern feature is elongated nearly east-west, and a velocity gradient appeathat this feature is a jet-entrained gas. The eastern feature is elongated nearly east-west, and a velocity gradient appears with the opposite sense of that previously inferred for the putative disk. Possible explanations for the observed gas dirs with the opposite sense of that previously inferred for the putative disk. Possible explanations for the observed gas distribution & kinematics are that a rotating gas disk disturbed by the jet, streaming gas, or a ring with another smaller coustribution & kinematics are that a rotating gas disk disturbed by the jet, streaming gas, or a ring with another smaller counter- or Keplarian-rotating gas disk inside.nter- or Keplarian-rotating gas disk inside.

S. Beckwith (STScI), Hubble Heritage S. Beckwith (STScI), Hubble Heritage Team (STScI/AURA), ESA, NASATeam (STScI/AURA), ESA, NASA

Scoville et al. 1998Scoville et al. 1998ApJ, 493, L63ApJ, 493, L63

OVRO CO(2-1) ImageOVRO CO(2-1) ImageSpatial Resolution: 0.8”x1.2”Spatial Resolution: 0.8”x1.2”

Kohno et al. 1996 AKohno et al. 1996 ApJ, 461, L29pJ, 461, L29

IntroductionIntroduction M51 is one of the nearest Seyfert galaxies (7.1 Mpc; TakaM51 is one of the nearest Seyfert galaxies (7.1 Mpc; Takats & Vinko 2006) with type 2 AGN. A pair of radio jets emats & Vinko 2006) with type 2 AGN. A pair of radio jets emanates from the nucleus, and narrow line regions (NLRs) are nates from the nucleus, and narrow line regions (NLRs) are associated with the jet (e.g., Bradley et al. 2004). Interferoassociated with the jet (e.g., Bradley et al. 2004). Interferometric images in molecular gas show blueshifted emission metric images in molecular gas show blueshifted emission on the eastern side of the nucleus, and redshifted gas on thon the eastern side of the nucleus, and redshifted gas on the western side (right figures). This shift is almost perpendice western side (right figures). This shift is almost perpendicular to the jet axis, and the estimated column density is conular to the jet axis, and the estimated column density is consistent with that estimated from X-ray absorption toward the sistent with that estimated from X-ray absorption toward the nucleus, suggesting that the molecular gas can benucleus, suggesting that the molecular gas can be

a rotating disk and play an important role in obscuring the AGN. However, SMA CO(3-2) observations suggest a velocia rotating disk and play an important role in obscuring the AGN. However, SMA CO(3-2) observations suggest a velocity gradient along the jet in addition to that perpendicular to the jet (Matsushita et al. 2004), which imply more complicatty gradient along the jet in addition to that perpendicular to the jet (Matsushita et al. 2004), which imply more complicated features than a simple disk structure. We therefore performed sub-arcsecond resolution CO(2-1) & CO(1-0) imagined features than a simple disk structure. We therefore performed sub-arcsecond resolution CO(2-1) & CO(1-0) imaging observations of the center of M51 with IRAM PdBI to study the distribution and kinematics of the molecular gas aroung observations of the center of M51 with IRAM PdBI to study the distribution and kinematics of the molecular gas around the AGN in more detail.d the AGN in more detail.

Bradley et al. 2004, ApJ, 603, 463Bradley et al. 2004, ApJ, 603, 463

[OIII] image overlaid on[OIII] image overlaid onVLA 3.6cm continuum contourVLA 3.6cm continuum contour CO(2-1) velocityCO(2-1) velocity

Black dots:Black dots:[OIII] velocity[OIII] velocity& its dispersion& its dispersion

CO(2-1) ImageCO(2-1) ImageHST 439nm ImageHST 439nm Image(Archival Data)(Archival Data)

Molecular Gas Distribution & KinematicsMolecular Gas Distribution & Kinematics Left images show CO(2-1) distribution near the Seyfert 2 nuclLeft images show CO(2-1) distribution near the Seyfert 2 nucleus. The synthesized beam sizes reached to 0.40” x 0.31” (14 eus. The synthesized beam sizes reached to 0.40” x 0.31” (14 pc x 11 pc). The overall distribution and kinematics are consistpc x 11 pc). The overall distribution and kinematics are consistent with past observations, if we degrade our image to lower anent with past observations, if we degrade our image to lower angular resolution. Our images, however, show more complicategular resolution. Our images, however, show more complicated structures and kinematics, and no clear evidence of the previd structures and kinematics, and no clear evidence of the previous suggested circumnuclear disk/torus. Molecular gas on the ous suggested circumnuclear disk/torus. Molecular gas on the western side of the nucleus is elongated along the radio jet, anwestern side of the nucleus is elongated along the radio jet, and the velocity gradient is also parallel to the jet. The molecular d the velocity gradient is also parallel to the jet. The molecular gas velocity matches well with the velocity of the [OIII] emission gas velocity matches well with the velocity of the [OIII] emission from the NLRs (see figures below), suggesting that the moleculfrom the NLRs (see figures below), suggesting that the molecular gas is entrained by the jet. In addition, some of the material iar gas is entrained by the jet. In addition, some of the material in NLRs may be supplied from molecular gas close to the AGN.n NLRs may be supplied from molecular gas close to the AGN.

CO(2-1) contour overlaid on VLA 6cm continuum imageCO(2-1) contour overlaid on VLA 6cm continuum image

VLA: Crane & van der Hulst 1992, AJ, 103, 1146VLA: Crane & van der Hulst 1992, AJ, 103, 1146

34 pc34 pc

Column Density toward the Seyfert 2 NucleusColumn Density toward the Seyfert 2 Nucleus Molecular gas column density estimated from CO(2-1) iMolecular gas column density estimated from CO(2-1) indicates 6.2 x 10ndicates 6.2 x 102121 cm cm-2-2, but that estimated from X-ray ob, but that estimated from X-ray observations is 5.6 x 10servations is 5.6 x 102424 cm cm-2-2 (Fukazawa et al. 2001), whi (Fukazawa et al. 2001), which has 3 orders of magnitude difference. This discrepanch has 3 orders of magnitude difference. This discrepancy can be explained by (1) dilution effect, if obscuring mcy can be explained by (1) dilution effect, if obscuring material locates much closer to the nucleus or in a very thiaterial locates much closer to the nucleus or in a very thin disk, or (2) obscuring material that cannot be seen in Cn disk, or (2) obscuring material that cannot be seen in CO(2-1). It maybe possible to see in higher-J lines (e.g., CO(2-1). It maybe possible to see in higher-J lines (e.g., CO J=3-2) or denser gas tracers (e.g., HCN).O J=3-2) or denser gas tracers (e.g., HCN).

Does Molecular Gas Torus/Disk exist around the M51 Seyfert 2 NuclDoes Molecular Gas Torus/Disk exist around the M51 Seyfert 2 Nucleus?eus? From our data set, it is not clear whether there is a molecular gas disk/torus arFrom our data set, it is not clear whether there is a molecular gas disk/torus around the Seyfert 2 nucleus of M51 with the spatial scale of 10 pc or larger. So ound the Seyfert 2 nucleus of M51 with the spatial scale of 10 pc or larger. So what are these molecular gas structures we observed? One possibility is that twhat are these molecular gas structures we observed? One possibility is that these are the remnants of a circumnuclear disk, but disturbed by the radio jet. hese are the remnants of a circumnuclear disk, but disturbed by the radio jet. Other possibility is that there is a ring with a radius of 30-40 pc, and another smOther possibility is that there is a ring with a radius of 30-40 pc, and another smaller counter- or Keplarian-rotating disk inside. This rather complicated structuraller counter- or Keplarian-rotating disk inside. This rather complicated structure is supported by the Hubble Space Telescope (HST) images of the nuclear ree is supported by the Hubble Space Telescope (HST) images of the nuclear region of M51 (left images), which show X-shape dark lanes in front of the nucleugion of M51 (left images), which show X-shape dark lanes in front of the nucleus. It is also possible that these structures are totally independent, and the wests. It is also possible that these structures are totally independent, and the western gas is jet-entrained structure, and the eastern gas can be streaming gas toern gas is jet-entrained structure, and the eastern gas can be streaming gas toward the nucleus.ward the nucleus.