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Journal Article•DOI•

Absolute spectrophotometry in M31 and M32

J. B. Oke, M. Schwarzschild
15 May 1975-The Astrophysical Journal-Vol. 198, pp 63-70
TL;DR: For a number of places in the bulge of M31 and for two places in M32, photometric scans from lambda = 3300 A to lambda = 10,600 A have been obtained with the multichannel spectrometer on the 5m Hale telescope as discussed by the authors.
Abstract: For a number of places in the bulge of M31, and for two places in M32, photometric scans from lambda = 3300 A to lambda = 10,600 A have been obtained with the multichannel spectrometer on the 5-m Hale telescope. The scans show that in both objects the color temperature (particularly shortward of 5000 A) decreases toward the center, and that the strength of the CN bands increases toward the center in both objects, in agreement with other earlier observations. The new data can all be interpreted in terms of an increase of heavy-element abundance toward the center in both objects by a factor probably less than 2, and by an excess of heavy elements in M31 compared with M32 by a factor probably greater than 2, in qualitative agreement with earlier conclusions of other observers.

Summary (1 min read)

Jump to:  and [INTRODUCTION]

INTRODUCTION

  • Alt}iough the instrument has both a star and sky aperture separated by 40 `, this is not useful for sky subtraction in extended hence objects;/the instrument was used either without the starsky chopper running, or by reducing data i n the two apertures completely separately.
  • There is some suggestion that changes in the CN band strengths are smaller than in the previous case.
  • Indeed the color difference turns out to be 0.04 mag, hard at the margin of measurability with the present data.
  • Altogether then, these observations give for the entire bulge of M31 a progressive reddening of the spectral gradient as one approaches the center, the spectral changes being minor in the outer portions of the bulge but increasing rapidly towards the center -quite parallel to the strength of the CN features (Spinrad et al. 1971 ).

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Produced by the NASA Center for Aerospace Information (CASI)
ABSOLUTE SPECTROPHOTOMETRY IN M31 AND M32
J. B. Oke
Hale Observatories, California Institute of Ter7hnology
Carnegie Institution of Washington
and
M. Schwarzschild*
Princ^zton University Observatory
Received:
(21?,SA-CR-140683) ABSOLUTE
N75-10879
S E^
rD
OPHOTOMZTRY IN H31 AND M32 (Hale
Observatories, Pasadena, Cal.if.) 25 p HC
—(
$3.25
CsCL 03A
Unclas
G3/89 53609
*Visiting Sherman Fairchild Distinguished Scholar,
California Institute of Te.
i
hnology
a
17
1
1
ABSTRACT
For a number of places in the bulge of M31 and for
two places in M32 photometric scans from
1
= 3300
A
to
have been obtained with the multichannel
slpectrometer"'on"the 5-meter Hale telescope.
The scans
-
show that,in both objects the color temperature
(particularly shortwards of 5000
A)
decreases towards
the center and that the strength of the CN bands increases
--
towards the center in both objects in agreement with
arlier observations.
The new data can all be interpreted
in terms of an increase of heavy element abundance
towards the
-
center in both objects by a factor- probably-
less than 2 and by an excess of heavy elements in M31
compared to M32 by a factor probably greater than 2, in
qualitative agreement with earlier conclusions.
S
ubject Headings:
GALAXIES,
SPECTROPHOTOMETRY, ABUNDANCES
3
y.
I'
2
I
INTRODUCTION
It has been known for many years that some galaxies
show a charge of color with distance from the center (Tifft
1961, 1963, de Vaucouleurs 1961, Hodge 1963). Sandage,
P.ecklin, and Neugebauer (1969) have shown that ultraviolet
color changes occur in M31 within 20
`
of the center. They
also report a color change in M32 which depends on distance
from the
center.
The 6-color photometry of Stebbins and
Whitford (1948) demonstrated that over a wide spectral
range M31 and M32 had different energy distributions.
This was also shown by Oke (1962) using detailed scars.
In recent years-most of the observational work on
M31 and M32 has concentrated on measuring various line
— —
strengths or indices to study the metallicity in the
objects. We mention as examples the work of McClure
and Van den Bergh (1968), McClure (1969), Spinrad and
Taylor (1971), Spinra3 et al. (1971), Spinrad et al.(1972),
Joly dnd A,ndrillat {1973) .
In order to investigate in more detail the known color
changes with distance from the center of M31 and M32,
detailed energy distributions covering the wavelength
range for
X
3300 to X10,600 have been obtained in the
bulge of M31 and at two points in M32. Enough detail
is present in some cases to make comments not only on the
overall energy distributions but also on the strengths
of features such as the CN bands.
3
OBSERVATIONS
All the observations were made with the multichannel
spectrometer attached to the 5-meter Hale telescope. Alt}iough
the instrument has both a star and sky aperture separated
by 40
`
, this is not useful for sky subtraction in extended
hence
objects;/the instrument was used either without the star-
sky chopper running, or by reducing data
i
n the two apertures
completely separately. Sky measurements were made well
outside of M31 and M32.
It was the original intention to measure separately
the tiny 3
:
5 diameter nucleus of M31; however, atmospheric
refraction effects were too large. All results given in
this paper refer to a round aperture of radius 5^. Energy
distributions are based on the absolute calibration of
a Lyrae as given by Oke and Schild
(
1970) and results are given
in terms of AB = -2.5 log f
.
-
48.60 when f is the flux in
ergs s
-1
cm
2
Hz-l.
The highest resolution measurements, using a bandpass
of 40 A in the blue (1/k > 1.74) and 80 A in the red,
are given in table 1. Along with 1/a, where a is the
wavelength measured
-Ji
r'microns, are the fluxes in the
i
center of M31,'oitoin a radius of 5% and the fluxes
in a 5
`
radio:.' .
.
erture 40
0
East of the center. The
resulting absolute fluxes
,
in the form
AB, for the
Citations
More filters
Journal Article•DOI•
Stellar populations of early-type galaxies in different environments - III. Line-strength gradients

[...]

Patricia Sanchez-Blazquez1, Patricia Sanchez-Blazquez2, Javier Gorgas2, Nicolás Cardiel2•
École Polytechnique Fédérale de Lausanne1, Complutense University of Madrid2
01 Oct 2006-Astronomy and Astrophysics
TL;DR: In this paper, the authors studied the stellar content of early-type galaxies and derived the age and metallicity gradients for 22 spectral indices measured in a sample of 82 early type galaxies in different environments, including the high density cores of the Coma cluster, the Virgo cluster, poor groups, and isolated field galaxies.
Abstract: Aims This is the third paper of a series devoted to the study of the stellar content of early-type galaxies The goal of the series is to set constraints on the evolutionary status of these objects Methods We present line-strength gradients for 22 spectral indices measured in a sample of 82 early-type galaxies in different environments, including the high-density cores of the Coma cluster, the Virgo cluster, poor groups, and isolated field galaxies Using new evolutionary population synthesis models, we derive age and metallicity gradients, and compare the mean values with the predictions of different galaxy formation models We explore the behaviour of individual chemical species by deriving the metallicity gradient with different indicators Results We find that the strength of the metallicity gradient inferred from stellar population models depends on the specific Lick index employed In particular, metallicity gradients obtained with CN2 and C4668 combined with H beta are steeper than those measured using Ca4227 or Fe4383 The correlation of the metallicity gradients with other parameters also depends on the specific index employed If the metallicity gradient is obtained using CN2 and Mgb, then it correlates with the central age of the galaxies On the contrary, if Fe4383 or Ca4227 is used, the metallicity gradient correlates with the velocity dispersion gradient Conclusions This may suggest that several mechanisms have helped to set the age and metallicity gradients in early-type galaxies While we do not find any correlation between the metallicity gradient and the central velocity dispersion for galaxies in low-density environments, we find a marginal correlation between the metallicity gradient and the mass for galaxies in the centre of the Coma cluster We also find a trend for which galaxies in denser environments show a steeper metallicity gradient than galaxies in less dense environments We interpret these results in light of the different mechanisms proposed to explain the observed changes between galaxies as a function of environment

79 citations

Journal Article•DOI•
The stellar content of elliptical nuclei

[...]

Sandra M. Faber
01 Jan 1983-Highlights of Astronomy
TL;DR: In this article, it has been shown that the source of the excess UV light is not young OB stars, but rather a large number of old stellar populations in elliptical galaxies.
Abstract: New developments in understanding the stellar populations of ! elliptical nuclei are discussed. Variations in iron-peak spectral j features have recently been detected, which are much smaller than \\ changes in CN, Mg, and Na. A study is presently in progress to I determine whether this pattern is consistent with lockstep enhancements j in all heavy elements. Present evidence on the ultraviolet spectra of | ellipticals now suggests that the source of the excess UV light is not I young OB stars. A new correlation is also pointed out between UV j excess and mean line strength. If real, this trend is further evidence j against significant numbers of young OB stars in elliptical galaxies. j To first approximation, only two physical parameters are needed to j characterize the spectra of old stellar populations, namely stellar I age (or rate of star formation versus time) and composition. My j remarks today concern these two quantities as they apply to ellipticalI galaxy populations. Consider composition first. It has long been known that E-galaxy spectra exhibit a sequence in line strength and color, exemplified both by variations among galaxies and by radial gradients within j galaxies. As with the phenomenologically similar trend among globular \\ clusters, this sequence has conventionally been interpreted in terms of metallicity variations. Attempts to calibrate the sequence in terms of iron abundance have typically shown that the strongest-lined ellipticals are between two and four times more metal-rich than M32 (Faber 1973; Oke and Schwarzschild 1975; Larson and Tinsley 1974; Cohen 1979). A weakness of these previous calibrations, however, is the fact that they depend largely on the very large line-strength changes seen only in CN, Mg, and Na. No iron-peak features have as yet been used. Counter to the usual metallicity interpretation, a few authors have proposed instead that only the elements N, Mg, and Na are changing

33 citations

Journal Article•DOI•
First detection of cold dust in the northern shell of NGC5128 (Centaurus A)

[...]

Manfred Stickel1, J. M. van der Hulst2, J. H. van Gorkom3, David Schiminovich4, Chris Carilli5 •
Max Planck Society1, Kapteyn Astronomical Institute2, Columbia University3, California Institute of Technology4, National Radio Astronomy Observatory5
01 Feb 2004-Astronomy and Astrophysics
TL;DR: In this article, the authors used deep far-infrared (FIR) imaging data obtained with ISOPHOT at 90 mum, 150 mum, and 200 mum to detect the thermal emission from cold dust in the northern shell region of NGC5128 (Centaurus A).
Abstract: Deep far-infrared (FIR) imaging data obtained with ISOPHOT at 90 mum, 150 mum, and 200 mum detected the thermal emission from cold dust in the northern shell region of NGC5128 (Centaurus A), where previously neutral hydrogen and molecular gas has been found. A somewhat extended FIR emission region is present in both the 150 mum and 200 mum map, while only an upper flux limit could be derived from the 90 mum data. The FIR spectral energy distribution can be reconciled with a modified blackbody spectrum with very cold dust color temperatures and emissivity indices in the range 13K beta > 1, respectively, where the data favor the low temperature end. A representative value for the associated dust mass is M(Dust) approximate to 7 x 10(4) M(.), which together with the HI gas mass gives a gas-to-dust ratio of approximate to300, close the average values of normal inactive spiral galaxies. This value, in conjunction with the atomic to molecular gas mass ratio typical for a spiral galaxy, indicates that the interstellar medium (ISM) from the inner part of a captured disk galaxy is likely the origin of the outlying gas and dust. These observations are in agreement with recent theoretical considerations that in galaxy interactions leading to stellar shell structures the less dissipative clumpy component of the ISM from the captured galaxy can lead to gaseous shells. Alternatively, the outlying gas and dust could be a rotating ring structure resulting from an interaction or even late infall of tidal material of a merger in the distant past. With all three components ( atomic gas, molecular gas, dust) of the ISM present in the northern shell region, local star formation may account for the chains of young blue stars surrounding the region to the east and north. The dust cloud may also be involved in the disruption of the large scale radio jet before entering the brighter region of the northern radio lobe.

30 citations

Journal Article•DOI•
The jet/wind outflow in Centaurus A: A local laboratory for AGN feedback

[...]

Benjamin McKinley1, Benjamin McKinley2, Steven Tingay1, Ettore Carretti3, Simon Ellis4, Joss Bland-Hawthorn5, R. Morganti6, R. Morganti7, J. L. B. Line1, J. L. B. Line2, Michael McDonald8, Sylvain Veilleux9, R. Wahl Olsen, M. Sidonio, Ron Ekers10, Ron Ekers1, A. R. Offringa7, Pietro Procopio1, Pietro Procopio2, Bartosz Pindor1, Bartosz Pindor2, Randall B. Wayth1, Natasha Hurley-Walker1, Gianni Bernardi11, Bryan Gaensler1, Bryan Gaensler12, Marijke Haverkorn13, M. J. Kesteven10, Sergio Poppi3, Lister Staveley-Smith1, Lister Staveley-Smith14 •
Curtin University1, University of Melbourne2, INAF3, Australian Astronomical Observatory4, University of Sydney5, Kapteyn Astronomical Institute6, ASTRON7, Massachusetts Institute of Technology8, University of Maryland, College Park9, Commonwealth Scientific and Industrial Research Organisation10, Rhodes University11, University of Toronto12, Radboud University Nijmegen13, University of Western Australia14
01 Mar 2018-Monthly Notices of the Royal Astronomical Society
TL;DR: In this article, radio and optical images of the nearest radio galaxy Centaurus A and its host galaxy NGC 5128 are presented, where the authors focus their investigation on the northern transition region, where energy is transported from the similar to 5 kpc (similar to 5 arcmin) scales of the northern inner lobe (NIL) to the more distant northern middle lobe (nML) scales.
Abstract: We present new radio and optical images of the nearest radio galaxy Centaurus A and its host galaxy NGC 5128. We focus our investigation on the northern transition region, where energy is transported from the similar to 5 kpc (similar to 5 arcmin) scales of the northern inner lobe (NIL) to the similar to 30 kpc (similar to 30 arcmin) scales of the northern middle lobe (NML). Our Murchison Widefield Array observations at 154 MHz and our Parkes radio telescope observations at 2.3 GHz show diffuse radio emission connecting the NIL to the NML, in agreement with previous Australia Telescope Compact Array observations at 1.4 GHz. Comparison of these radio data with our wide-field optical emission-line images show the relationship between the NML radio emission and the ionized filaments that extend north from the NIL, and reveal a new ionized filament to the east, possibly associated with a galactic wind. Our deep optical images show clear evidence for a bipolar outflow from the central galaxy extending to intermediate scales, despite the non-detection of a southern radio counterpart to the NML. Thus, our observational overview of Centaurus A reveals a number of features proposed to be associated with active galactic nucleus feedback mechanisms, often cited as likely to have significant effects in galaxy evolution models. As one of the closest galaxies to us, Centaurus A therefore provides a unique laboratory to examine feedback mechanisms in detail.

30 citations

Journal Article•DOI•
Is the polarization of NGC1068 evidence for a non-thermal source

[...]

I. S. McLean1, C. Aspin1, S. R. Heathcote1, M. J. McCaughrean1•
University of Edinburgh1
01 Aug 1983-Nature
TL;DR: In this article, it was shown that dilution by starlight modifies the polarization to an extent not previously appreciated, and that the polarization of the non-stellar flux in the optical and near IR is approximately independent of wavelength with a direction orthogonal to that of the radio jets.
Abstract: NGC1068 is one of the brightest galaxies included by Seyfert1 in his list of extragalactic objects having compact, luminous nuclei within which broad, high-excitation emission lines occur. It has been the subject of intensive studies at UV2,3, optical3–6, IR7–12 and radio wavelengths13–15. Unresolved questions concern the nature and relationship of the sources of the excess flux seen in the UV and IR, their connection with the collimated jets apparent in high-resolution radio maps and their association with the extended region responsible for the broad emission lines. A further question is the location of any dust and its role in modifying the optical and UV spectrum. We report here observations with two high-resolution optical spectro-polarimeters which throw new light on these questions. From detailed structure found in the linear polarization spectrum of the nucleus we conclude that dilution by starlight modifies the polarization to an extent not previously appreciated. In fact, the polarization of the non-stellar flux in the optical and near IR is approximately independent of wavelength (as expected for synchrotron emission or electron scattering) with a direction orthogonal to that of the radio jets; such an arrangement is reminiscent of certain quasars and radio galaxies16,17.

9 citations

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