Ionized gas in the center of M31

Jacoby, George H.; Ford, Heath; Ciardullo, Robin

doi:10.1086/162968

Cited by 46 publications

(63 citation statements)

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“…There are two features, which can be clearly distinguished in the SI map: the inner 400 pc and the southern arm, known from Hα observations (e.g. Jacoby et al 1985). The spectral index in the very centre is −0.40±0.03 and steepens outwards where it quickly reaches values of −1.0 and steeper.…”

Section: Combination With Effelsberg Datamentioning

confidence: 95%

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The magnetic field structure of the central region in M 31

Gießübel

Beck

2014

A&A

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Context. The Andromeda Galaxy (M 31) is the nearest grand-design spiral galaxy. Thus far, most studies in the radio regime concentrated on the 10 kpc ring. The central region of M 31 has significantly different properties than the outer parts: The star formation rate is low, and inclination and position angle are largely different from the outer disk. Aims. The existing model of the magnetic field in the radial range 6 ≤ r ≤ 14 kpc is extended to the innermost part r ≤ 0.5 kpc to ultimately achieve a picture of the entire magnetic field in M 31. Methods. We combined observations taken with the VLA at 3.6 cm and 6.2 cm with data from the Effelsberg 100-m telescope to fill the missing spacings of the synthesis data. The resulting polarization maps were averaged in sectors to analyse the azimuthal behaviour of the polarized intensity (PI), rotation measure (RM), and apparent pitch angle (φ obs ). We developed a simplified 3D model for the magnetic field in the central region to explain the azimuthal behaviour of the three observables.Results. Our 3D model of a quadrupolar or dipolar dynamo field can explain the observed patterns in PI, RM, and φ obs , while a 2D configuration is not sufficient to explain the azimuthal behaviour. In addition and independent of our model, the RM pattern shows that the spiral magnetic field in the inner 0.5 kpc points outward, which is opposite to that in the outer disk, and has a pitch angle of 33 • , which is much larger than that of 8• in the outer disk. Conclusions. The physical conditions in the central region differ significantly from those in the 10 kpc ring. In addition, the orientation of this region with respect to the outer disk is completely different. The opposite magnetic field directions suggest that the central region is decoupled from the outer disk, and we propose that an independent dynamo is active in the central region.

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Section: Combination With Effelsberg Datamentioning

confidence: 95%

“…The strength of the radio synchrotron emission from the central region raises the question of the origin of cosmic rays in that region. Particle acceleration by magnetic reconnection near the galaxy's centre (Lesch & Reich 1992) or in shock fronts possibly seen in Hα emission (Jacoby et al 1985) are under discussion.…”

Section: Introductionmentioning

confidence: 99%

The magnetic field structure of the central region in M 31

Gießübel

Beck

2014

A&A

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“…However, ionised gas is detected in the central field (e.g., Rubin & Ford 1971;Ciardullo et al 1988;Boulesteix et al 1987;Bogdán & Gilfanov 2008;Liu et al 2010), usually interpreted in term of shocks, and Melchior et al (2000) has detected only a small amount of molecular gas (1.5 × 10 4 M ) within 1.3 (305 pc in projection). There is no obvious on-going star formation in this central region (e.g., Olsen et al 2006;Li et al 2009;Azimlu et al 2011) and the ionised gas (approximately 1500 M according to Jacoby et al 1985) can be accounted for by mass lost from evolving stars.…”

Section: Introductionmentioning

confidence: 98%

Molecular gas in the inner 0.7 kpc-radius ring of M 31

Melchior

Combes

2011

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The study of the gas kinematic in the central 1.5 kpc × 1.5 kpc region of M 31 has revealed several surprises. The starting point of this investigation was the detection at the IRAM-30 m telescope of molecular gas with very large line splittings up to 260 km s −1 within the beam (∼40 pc). In this region, which is known for its low gas content, we also detect an ionised gas outflow in the circumnuclear region (within 75 pc from the centre) extending to the whole area in X-ray. Relying on atomic, ionised, and molecular gas, we account for most observables with a scenario that assumes that a few hundreds Myr ago, M 31 underwent a frontal collision with M 32, which triggered some star-formation activity in the centre, and this collision explains the special configuration of M 31 with two rings observed at 0.7 kpc and 10 kpc. The inner disc (whose rotation is detected in HI and ionised gas ([NII])) has thus been tilted (inclination: 43 deg, PA: 70 deg) with respect to the main disc (inclination: 77 deg, PA: 35 deg). One of the CO velocity components is compatible with this inner disc, while the second one comes from a tilted ring-like material with 40 deg inclination and PA = −35 deg. The relic star formation estimated by previous works to have occurred more than 100 Myr ago could have been triggered by the collision and could be linked to the outflow detected in the ionised gas. Last, we demonstrate that the amplitude of the line splittings detected in CO centred on the systemic velocity with a relatively high spatial resolution (40 pc) cannot be accounted for by a possible weak bar that is roughly aligned along the minor axis. Although M 31 has a triaxial bulge, there are no bar indicators in the gas component (photometry, no strong skewness of the isovelocities, etc.).

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“…The presence of a very massive black hole (Dressler 1984) and the lack of gas within 300 pc (Nieten et al 2006;Chemin et al 2009;Braun et al 2009) suggest that the main gas reservoir has been accreted and is exhausted, although some gas is detected within 1 kpc from the center (Melchior et al 2000;Melchior & Combes 2011). From optical emission lines Jacoby et al (1985) estimated an ionized gas mass on the order of 1500 M , which can be accounted for by mass loss from evolving stars. Groves et al (2012) relied on Herschel data to argue that the dust properties are well accounted for by the stellar heating.…”

Section: Introductionmentioning

confidence: 99%

A cold-gas reservoir to fuel the M 31 nuclear black hole and stellar cluster

Melchior¹,

Combes²

2012

A&A

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With IRAM-30 m/HERA, we have detected CO(2-1) gas complexes within 30 arcsec (∼100 pc) from the center of M 31 that amount to a minimum total mass of 4.2×10 4 M (one third of the positions are detected). Averaging the whole HERA field, we show that there is no additional undetected diffuse component. Moreover, the gas detection is associated with gas lying on the far side of the M 31 center as no extinction is observed in the optical, but some emission is present on infrared Spitzer maps. The kinematics is complex.(1) The velocity pattern is mainly redshifted: the dynamical center of the gas differs from the black hole position and the maximum of optical emission, and only the redshifted side is seen in our data. (2) Several velocity components are detected in some lines of sight. Our interpretation is supported by the reanalysis of the effect of dust on a complete planetary nebula sample. Two dust components are detected with respective position angles of 37 deg and -66 deg. This is compatible with a scenario where the superposition of the (PA = 37 deg) disk is dominated by the 10 kpc ring and the inner 0.7 kpc ring detected in infrared data, whose position angle (-66 deg) we measured for the first time. The large-scale disk, which dominates the HI data, is steeply inclined (i = 77 deg), warped and superposed on the line of sight on the less inclined inner ring. The detected CO emission might come from both components.

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Ionized gas in the center of M31

Cited by 46 publications

References 0 publications

The magnetic field structure of the central region in M 31

The magnetic field structure of the central region in M 31

Molecular gas in the inner 0.7 kpc-radius ring of M 31

A cold-gas reservoir to fuel the M 31 nuclear black hole and stellar cluster

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