J. Antonio Garcia-Barreto

Observations of Barred Galaxies

My recent work deals primarily with the observation of barred spiral galaxies, in particular bright, nearby galaxies from the Shapley-Ames catalog. The selected galaxies were chosen to have long infrared (from IRAS) colors indicative of star formation and some indication of circumnuclear structure in the visible.

I combine observations of radio continuum emission from the VLA at different wavelength, HI observations using Arecibo (305m diameter), Effelsberg (100m diameter), and CO (IRAM 30m diameter and SEST 15m diameter) and optical observations of the red continuum (R and I filters) and narrow band line (Halpha) emission and optical spectroscopy of the red part of the optical spectrum using the optical telescopes in San Pedro Martir, Mexico.

The standard model to explain circumnuclear sturctures uses the dynamics of star and gas under the influence of the non-axisymmetric gravitational field of a barred galaxy. The structures are thought to be formed at the so called Inner Lindblad Resonances (ILR).

Important observational parameters are: radii of the circumnuclear structures and the rotation velocity of the gas.

NGC 1022, NGC 1326 y NGC 4314
These galaxies were observed with the VLA at 2, 6, and 20 cm with an angular resolution of about 3''.5, of their CO emission using the SEST and IRAM telescopes and the JHK photometry using a single detector. In the case of NGC 4314 we carried out observations of its HI content using the Arecibo radio telescope. The references are: NGC 1022 (1991 A&A, 252, 19)[14], NGC 1326 (1991 RMxAA, 22, 197)[15], and NGC 4314 (1991 A&A, 244, 257) [12].

The mass of H2 in NGC 1326 was 220 million solar masses, 1,700 million solar masses of HI, 20 million solar masse sof ionized gas and 1,600 million of gravitational mass inside 180 pc. Co-rotation was taken as the end of the bar, that is,4 kpc, and the ILR between 200 and 400 pc. The angular velocity of the gas at the ILR was found to be 385 km/s/kpc and angular velocity of the bar was 60 km/s/kpc.

In the case of NGC 4314, the H2 mass was found to be 250 million solar masses, only 40 million solar masses of HI, 3 million solar masses of ionized gas and 2,000 million solar masses of gravitational mass inside 450 pc. Co-rotation was taken to be at 3.6 kpc, and the distance of the Inner Lindblad Resonance at 450 pc. The angular velocity at the ILR was found to be 246 km/s/kpc and the angular velocity of the bar was found to be 36 km/s/kpc.

No circumnuclear structure was found in NGC 1022. The three galaxies are of Hubble type SBa

CO from the Anomalous Arms in NGC 4258

We carried out observations of the CO emission from the anomalous arms in NGC 4258 with the IRAM 30m radio telescope in Spain. CO was found from the anomalous arms but no signal was detected beyond the arms. (1990 A&A, 233, L1)[11]

Radio Continuum Observations using the 100m Effelsberg Radio telescope

Observations of the radio continuum emission at 6.3 and 2.8 cm were carried out using the 100m radio telescope in Effelsberg, Germany. The angular resolution was 2.4 and 1.2 min of arc respectively. The observed galaxies were: NGC 2336, 2366, 2835, 2935, 3319, 3351, 3359, 3513, 3686, 3729, 3953, 3992, 4123, 4214, 4236, 4242, 4487, 4496, 4535, 4618, 4654, 4691, 4725, 4902, 4981, 5068, 5669, 5792, 5850, 5921, 6217, 6907, 7479, 7640, 7723 y 7741. The main purpose of the project was to determine the relative contribution of star formation processes through the determination of their spectral indexes. Fifty percent of the galaxies presented an spectral index less than -0.7 (the average of the spectral index from disks of galaxies) (1993 RMxAA, 25, 31) [16]

Observation of HI from the Galaxies in the Coma I Group

We determine the amount of neutral Hydrogen from the galaxies in the Coma I group, including NGC 41314 using the 100m Effelsberg radio telescope.

The main result combining observations from the Arecibo telescope (with an angular resolution of 3.3 minutes of arc) and the 100m Effelsberg telescope (with an angular resolution of 9.3 minutes de arc) is that NGC 4314 only has 40 million solar masses of HI. The other galaxies observed were NGC 4020, 4062, 4080, 4136, 4150, 4173, 4203, 4204, U7300, NGC 4245, 4251, 4274, 4278, 4283, 4308, 4310, 4314, 4359, 4393, 4414, 4448, 4455, 4494, U7673, NGC 4525, 4559, 4562, 4565, I242+28, NGC 4670, 4725, y 4747. 16 of the observed galaxies presented less HI masses compared to the expected gas masses according to their Hubble type and luminosities.

The interpretation of the observations suggests the existence of intergalactic gas in the center of the group. Ram pressure stripping could be responsible for loss of atomic gas (1994 A&A, 288, 705)[17]

NGC 4691: High Velocity Gas near the nucleus

NGC 4691 is an early type galaxy with a remarkable innermost structure. Up to now the exact position of the dynamical center has not been determined. Our optical continuum observations in the broadband filters R (6000 Angstroms) and I (8400 A) show four compact sources in the central region. The four sources are arranged two and two at the same declination and only differing from the other pair by about 2''. In right ascension they are separated by 12'' each member of the pair. The foru sources emmitcontinuum-free Halpha emission. From the relative intensities of each source in the R, I, and Halpha filters we deduce the position of the nucleus. This position needs to be confirmed with the kinematical center.

Our optical spectroscopic observations showed two spectra from NGC 4691 separated each other by 12''. One of the spectra shows the normal lines of [NII], Halpha and [SII] with narrow widths at half maximum. The systemic velocity coincides with previous reported values. The second spectra, however, shows a broad Halpha line shifted 500 km/s to blue velocities compared to the systemic velocity and presents a full width at half maximum of about 1200 km/s. Since there were no broad [SII] lines, we concluded that the emission is not from the nucleus of the galaxy but from a region nearby.

The interpretation of this broad Halpha line is that gas has been expulsed at high velocities as a result of the explosion of one or several supernovae, a process of evolution of massive stars embedded in dense material in the center of the galaxy (1995 ApJ, 451, 156) [18]. NGC 4691 is of Hubble type SB0 or SBa.

NGC 3367

NGC 3367 shows a remarkable semicircle of bright Halpha sources to the SW of the galaxy at a distance of about 10 kpc from the center. It is of Hubble type SBc and shows a bright bar at a position angle of 65 degrees east of north. Halpha was not detected from its bar. The Optical observations are reported in 1996 ApJ, 469, 138 [19].

The radio continuum emission from this galaxy shows two lobes straddling the nucleus in addition to emission from the disk of the galaxy. The emission from the disk of the galaxy is related to star formation processes and evolution (supernovae), however, the emission from the two lobes is not related to star formation processes. This conclusion is based on the small emission of Halpha and large radio emission from the lobes. The emission of one of the lobes is polarized and the spectral index indicates an optically thin syncrotron radiation. These results are based on VLA observations with 4''.5 angular resolution at 20 cm (1998 AJ, 116, 111)[22]. New VLA A array observations at 3.5 cm and 20 cm are in the process of being analized.

In Search of Circumnuclear Structures in Barred Galaxies

Observations of Halpha continuum-free imaging of bright barred spiral galaxies from the Shapley Ames catalog were conducted to search for the existence of more circumnuclear structures. The observations consisted in imaging the optical continuum in the R (6000 A) and I (8400 A) with broadband filters as well as imaging the emission of Halpha continuum-free using narrowband filters. The observations were done using the 2.1m telescope in San Pedro Martir, Mexico using a 1024 x 1024 pixels CCD camera. The 52 observed galaxies were: NGC 672, 1022, 1326, I 1953, NGC 1415, 1637, 1784, 1832, 2139, 2217, 2223, 2339, 2525, 2545, 2787, 2798, 2835, 3185, 3287, 3318, 3319, 3351, 3359, 3367, 3504, 3513, 3783, 3912, 4123, 4314, 4385, 4435, 4477, 4507, 4561, 4688, 4691, 5135, 5188, 5347, 5430, 5534, 5597, 5691, 5728, 5757, 5915, 6239, 6907, 6951, 7479 and I 5273.

We detected Halpha in circumnuclear regions in 10 galaxies: NGC 1326 (SBa), 1415(SBa), 3318(SBbc), 3351(SBb), 4314(SBa), 5135(SBb), 5347(SBb), 5430(SBb), 5728(SBb) y 6951(SBb).

We did not detect any Halpha emission from any galaxy classified as SBa (11 out of 52). 18 of 28 galaxies clasified as SBbc, SBc or SBlate showed central Halpha and 13 de 28 showed Halpha from their bar regions. A total of 32 galaxies showed central Halpha (1996 RMxAA, 32, 89)[20].

A main motivation of this work is to study the spatial distribution of ionized gas to understand the effects of the bar plus disk gravitational potential

I and Halpha Images of Barred Spiral Galaxies

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(Created: August 19, 1998. Updated: August 20, 1998)