Total Magnitudes of Virgo Galaxies. I.
Construction of a Self-consistent Reference Dataset
Spanning 8th to 18th mag.

Christopher Ke-shih Young
, PASA, 18 (2), in press.
Next Section: Bright-end consistency checks
Title/Abstract Page: Total Magnitudes of Virgo
Previous Section: Intermediate galaxy sample (14th-12th
Contents Page: Volume 18, Number 2

Bright galaxy sample (14th-8th mag.)

As already mentioned, existing CCD photometry of the brightest Virgo galaxies is generally susceptible to sky-subtraction problems, whilst photographic emulsions are of limited use because of their small dynamic range. One dataset that stands out from existing CCD and photographic ones is the `globally mapped' surface photometry of Caon et al. (1990 & 1994). This photometry couples wide-field photographic images, for which the sky can be determined accurately, with CCD images of the central parts of galaxies that are saturated on most photographic plates. Caon et al. (1990) presented two different sets of total-magnitude estimates: those listed in their Table I and those listed in their Table VI. Each Table I value was obtained by means of an integration to the relevant limiting isophote followed by an

$r^{\frac{1}{4}}$-law extrapolation (based only on the outer few isophotes of each luminosity profile) to an infinite radial distance. Each Table VI value on the other hand, was obtained by integration only, but this time to a relatively large radial distance greater than that of the limiting isophote of the published photometry. This latter distance was set as the point at which the surface brightness of the galaxy would fall to $\mu_B = 32$ mag.arcsec-2 if the

$r^{\frac{1}{4}}$-law extrapolation (used to generate its Table I value) were an accurate description of the unmeasurable outer parts of the galaxy profile. The total magnitudes presented by Caon et al. (1994) were derived in the same way as Caon et al.'s (1990) Table VI values. With a view to generating self-consistent t-system magnitudes independent of any

$r^{\frac{1}{4}}$-law assumption, it was decided to derive new total-magnitude estimates from Caon et al.'s (1990, 1994) original surface-brightness profiles. This was done by integrating the actual light curves numerically between the galaxy centroids r=0 and the faintest isophotes

$r=r_{{\rm max}}$, where r represents azimuthally averaged radial distance. In order to maximise the accuracy of these integrations, the profiles were interpolated in linear-distance-linear-intensity space (rather than

$r^{\frac{1}{4}}$-magnitude space in line with the units listed); and using Hill's (1982) interpolation routine INTEP. Note that the surface-brightness profiles of even the largest giants extended to large enough radial distances so as to include a substantial proportion of any halo light. The profile of NGC 4406 (=M86) for example, extended out to a radial distance of 10.4 arcmin.

Table 3: Improved total magnitude values (bold type) derived in this paper from a re-analysis of Caon et al.'s (1990 & 1994) surface-brightness profiles; the hitherto undefined quantities $\epsilon $, $\mu _{B_0}$, and r0, being ellipticity, Sérsic-model extrapolated central surface brightness and Sérsic-model scalelength respectively
Designation VCC type/

$B_{r<r_{{\rm max}}}$

 $r_{{\rm max}}$ $\epsilon $ $\mu _{B_0}$ n r0 Bt(syst.) Bt(integ.) $\Delta B$
  membership (mag.) (arcsec) (mag.arcesc-2) (arcsec) (mag.) (mag.) (mag.)
1990 data:
IC 3468 E/M 14.10 57.63 0.24 19.60 0.53 0.1817E+01 13.97 13.97 0.13
IC 3540 S0/M 14.77 31.18 0.12 19.39 0.72 0.2343E+01 14.64 14.72 0.05
IC 3653 E/M 14.56 27.06 0.06 18.42 0.64 0.1277E+01 14.53 14.53 0.03
IC 3773 d:S0/M 14.11 63.50 0.58 18.47 0.45 0.6294E+00 14.03 14.04 0.08
NGC 4168 E/M 12.34 110.08 0.24 16.09 0.28 0.4401E-01 12.05 12.05 0.29
NGC 4200 S0/M 14.01 47.25 0.41 17.74 0.42 0.3693E+00 13.90 13.89 0.11
NGC 4352 S0/M 13.56 68.08 0.38 17.33 0.40 0.3009E+00 13.50 13.49 0.07
NGC 4374 E/M 10.10 329.17 0.07 9.81 0.15 0.4891E-05 9.69 9.71 0.40
NGC 4387 E/M 13.16 85.61 0.24 16.24 0.38 0.1708E+00 13.14 13.13 0.03
NGC 4406 S0/M 9.79 484.53 0.40 11.59 0.15 0.1423E-04 9.15 9.15 0.64
NGC 4415 d:E/M 13.89 56.30 0.16 19.45 0.54 0.1967E+01 13.76 13.76 0.13
NGC 4417 S0/M 12.01 125.19 0.30 14.06 0.28 0.1835E-01 11.93 11.95 0.06
NGC 4431 dS0/M 14.21 43.50 0.33 19.84 0.54 0.2153E+01 13.96 13.96 0.25
NGC 4434 E-S0/M 13.18 65.63 0.14 14.94 0.30 0.2629E-01 13.06 13.08 0.10
NGC 4436 dE-dS0/M 14.15 62.06 0.41 18.65 0.42 0.5357E+00 14.00 14.01 0.14
NGC 4452 S0/M 12.86 95.38 0.60 17.88 0.48 0.1011E+01 12.89 12.83 0.03
NGC 4458 E/M 13.07 80.72 0.01 15.32 0.29 0.2641E-01 12.94 12.94 0.12
NGC 4459 S0/M 11.21 197.98 0.19 15.12 0.30 0.6466E-01 11.29 11.15 0.06
NGC 4464 E/M 13.53 47.53 0.07 15.05 0.36 0.6574E-01 13.46 13.49 0.04
NGC 4473 E/M 11.15 231.09 0.39 12.34 0.22 0.1525E-02 11.06 11.07 0.08
NGC 4474 S0/M 12.50 99.85 0.20 15.83 0.33 0.9517E-01 12.43 12.42 0.08
NGC 4476 S0/M 13.16 90.77 0.15 15.42 0.30 0.3278E-01 13.07 13.09 0.07
NGC 4478 E/M 12.42 63.42 0.08 16.78 0.50 0.8680E+00 12.39 12.39 0.04
NGC 4486 E/M 9.71 410.42 0.35 14.43 0.23 0.1314E-01 9.43 9.43 0.27
NGC 4550 E-S0/M 12.60 71.24 0.68 17.61 0.57 0.1665E+01 12.58 12.57 0.02
NGC 4551 E/M 13.11 62.71 0.21 17.56 0.50 0.9137E+00 13.07 13.08 0.03
NGC 4552 S0/M 10.80 245.11 0.17 9.32 0.15 0.2717E-05 10.47 10.48 0.32
NGC 4564 E/M 12.12 109.83 0.40 14.92 0.32 0.6149E-01 12.07 12.07 0.06
NGC 4578 S0/M 12.46 108.71 0.25 15.39 0.28 0.2836E-01 12.32 12.31 0.15
NGC 4621 E/M 10.63 310.37 0.09 9.87 0.15 0.3820E-05 10.29 10.30 0.34
NGC 4638 S0/M 12.16 82.43 0.38 16.07 0.45 0.5002E+00 12.13 12.14 0.02
NGC 4660 E-S0/M 12.14 90.29 0.16 12.73 0.26 0.5285E-02 12.06 12.07 0.07
1994 data:
NGC 4215 S0/M 12.92 54.25 0.61 17.02 0.48 0.6589E+00 12.95 12.88 0.05
NGC 4255 S0/M 13.69 48.36 0.38 15.92 0.38 0.1180E+00 13.63 13.64 0.04
NGC 4261 E/M 11.35 171.60 0.25 12.61 0.19 0.3345E-03 10.99 11.00 0.36
NGC 4268 S0/M 13.74 46.08 0.44 17.58 0.52 0.7694E+00 13.70 13.70 0.03
NGC 4269 S0/M 13.86 50.93 0.21 9.74 0.15 0.8938E-06 13.31 13.38 0.48
NGC 4270 S0/M 13.20 60.02 0.45 17.69 0.54 0.1146E+01 13.17 13.17 0.03
NGC 4339 S0/M 12.56 98.48 0.12 15.82 0.30 0.5332E-01 12.41 12.41 0.15
NGC 4342 S0/M 13.22 39.99 0.23 11.72 0.26 0.2078E-02 13.08 13.17 0.06
NGC 4360 E/B 13.69 88.99 0.18 15.88 0.30 0.3175E-01 13.60 13.61 0.07
NGC 4365 E/M 10.72 210.48 0.32 12.82 0.19 0.5118E-03 10.28 10.28 0.43
NGC 4377 S0/M 12.79 64.20 0.18 15.32 0.35 0.9057E-01 12.72 12.73 0.07
NGC 4472 E-S0/M 9.21 622.25 0.15 13.38 0.20 0.2295E-02 8.93 8.93 0.28
NGC 4570 S0-E/M 11.85 65.71 0.69 15.87 0.42 0.4143E+00 11.77 11.77 0.08
NGC 4600 S0/M 13.60 64.94 0.16 19.56 0.67 0.3684E+01 13.56 13.56 0.04
NGC 4623 E/M 13.26 66.19 0.55 18.09 0.47 0.9093E+00 13.18 13.18 0.08
NGC 4636 E-S0/M 10.31 288.01 0.35 14.59 0.21 0.4698E-02 9.79 9.79 0.52

                   
  • Notes: (1) Membership assignments are based on radial velocities: M (for member) if less than 3500 km ${\rm s}^{-1}$; otherwise B (for background). (2) Bt(syst.) represents systemic total magnitudes derived by integrating the best fitting profile parameters from r=0 to $\infty$. (3) Bt(integ.) represents the sum of

    $B_{r<r_{{\rm max}}}$ and the integral of the best fitting profile parameters from

    $r=r_{{\rm max}}$ to $\infty$. (4)

    $\Delta B = B_{r<r_{{\rm max}}}-B_t$(integ.). (5) For the sake of consistency, NGC 4215 was not treated differently from the other galaxies when its profile was fitted, even though it probably possesses a ring as noted by Caon et al. (1994). (6) NGC 4342 is also known as IC 3256.


We also re-fitted Caon et al.'s light curves with Davies et al.'s (1988) more natural form of Sérsic's law, ignoring isophotes flagged as unreliable and/or lacking ellipticity values. This yielded new global profile parameters for each galaxy which were then used for the extrapolation of each profile beyond the limiting isophote to an infinite radial distance. In practice, this involved integrating the best fitting Sérsic model from r=0 to $r=\infty$ analytically according to Equation 7 of Young et al. (1998); and also integrating the same model from r=0 to

$r=r_{{\rm max}}$ numerically using Simpson's rule. The extrapolation term required was therefore the difference between these two values. The improved total magnitude values together with all relevant profile parameters and extrapolation terms are listed in Table 3. Note that we omitted NGC 4649 because Caon et al. (1990) noticed that its isophotes were distorted by the presence of a companion galaxy. Also, in the case of Caon et al.'s (1994) profiles, we only fitted those 16 Virgo objects listed in Table (a) of the machine readable version at the CDS.

Next Section: Bright-end consistency checks
Title/Abstract Page: Total Magnitudes of Virgo
Previous Section: Intermediate galaxy sample (14th-12th
Contents Page: Volume 18, Number 2

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