Construction of a Self-consistent Reference Dataset
Spanning 8th to 18th mag.
Christopher Ke-shih Young
, PASA, 18 (2), in press.
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Title/Abstract Page: Total Magnitudes of Virgo
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Bright-end consistency checks
It is reassuring to find that for the 3 objects in common between Tablesá 2 and 3, the new total-magnitude values are in good agreement. For NGCá 4352, NGCá 4431 and NGCá 4436, the differences (Tableá 2 minus Tableá 3) are -0.01, +0.04 and +0.18 mag. respectively.Designation | VCC type/ | BT |
|
á | membership | (mag.) | (mag.) |
NGCá 4124 | S0/M | 12.10 | 0.42 |
NGCá 4168 | E/M | 12.25 | 0.45 |
NGCá 4262 | SB0/M | 12.43 | 0.16 |
NGCá 4267 | SB0/M | 11.81 | 0.47 |
NGCá 4339 | S0/M | 12.37 | 0.44 |
NGCá 4365 | E/M | 10.64 | 0.44 |
NGCá 4374 | E/M | 10.26 | 0.40 |
NGCá 4382 | S0(pec)/M | 10.03 | 0.33 |
NGCá 4387 | E/M | 12.97 | 0.22 |
NGCá 4406 | S0/M | 10.08 | 0.59 |
NGCá 4417 | S0/M | 12.02 | 0.27 |
NGCá 4425 | SBa/M | 12.75 | 0.18 |
NGCá 4429 | S0-Sa(pec)/M | 11.11 | 0.49 |
NGCá 4435 | SB0/M | 11.68 | 0.37 |
NGCá 4442 | SB0/M | 11.32 | 0.28 |
NGCá 4458 | E/M | 12.85 | 0.44 |
NGCá 4459 | S0/M | 11.39 | 0.43 |
NGCá 4461 | Sa/M | 12.08 | 0.31 |
NGCá 4472 | E-S0/M | 9.34 | 0.74 |
NGCá 4473 | E/M | 11.07 | 0.56 |
NGCá 4474 | S0/M | 12.57 | 0.29 |
NGCá 4476 | S0/M | 13.17 | 0.29 |
NGCá 4477 | SB0-SBa/M | 11.45 | 0.49 |
NGCá 4486 | E/M | 9.65 | 0.72 |
NGCá 4503 | Sa/M | 12.13 | 0.38 |
NGCá 4526 | S0/M | 10.70 | 0.15 |
NGCá 4550 | E-S0/M | 12.46 | 0.19 |
NGCá 4564 | E/M | 11.96 | 0.32 |
NGCá 4570 | S0-E/M | 11.79 | 0.24 |
NGCá 4596 | SBa/M | 11.50 | 0.44 |
NGCá 4638 | S0/M | 12.22 | 0.20 |
NGCá 4649 | S0/M | 9.88 | 0.80 |
á | á | á |
- Notes: (1) The
extrapolation values listed here are based on the maximum aperture for which a reliable measurement was obtained. (2) Membership assignments are based on radial velocities: M (for member) if less than 3500 km . (3) NGCá 4124 is not listed in the VCC. Its type was taken from the RC3 instead.
Designation | Tableá 3 | Michard | Caon et al. | Caon et al. | Caon et al. | Tableá 3 |
á | n | BT | BT (1990) Tableá I | BT (1990) Tableá VI | BT (1994) | Bt |
á | á | (mag.) | (mag.) | (mag.) | (mag.) | (mag.) |
NGCá 4261 | 0.19 | - | - | - | 11.03 | 11.00 |
NGCá 4269 | 0.15 | - | - | - | 13.32 | 13.38 |
NGCá 4365 | 0.19 | 10.64 | - | - | 10.35 | 10.28 |
NGCá 4374 | 0.15 | 10.26 | 10.26 | 9.71 | - | 9.71 |
NGCá 4406 | 0.15 | 10.08 | 10.06 | 9.63 | - | 9.15 |
NGCá 4472 | 0.20 | 9.34 | - | - | 8.87 | 8.93 |
NGCá 4473 | 0.22 | 11.07 | 11.10 | 11.02 | - | 11.07 |
NGCá 4486 | 0.23 | 9.65 | 9.58 | 9.48 | - | 9.43 |
NGCá 4552 | 0.15 | (10.91) | 10.78 | 10.38 | - | 10.48 |
NGCá 4621 | 0.15 | (10.83) | 10.76 | 10.30 | - | 10.30 |
NGCá 4636 | 0.21 | - | - | - | 10.01 | 9.79 |
- Notes: (1) Three objects were not observed by Michard: NGCá 4261, 4269 and 4636; whilst Michard's BT values for a further two are listed in parentheses because they were flagged by him as unreliable. Only the six objects for which Michard obtained reliable BT measurements appear on Fig.á 2. These objects are flagged with `' symbols.
In the cases of the six bright objects shown in Fig.á 2 for which n<0.25 then (see also Tableá 5), the large systematic differences between our new Bt values and Michard's BT ones cannot be the result of zero-point differences, but must primarily be due to the different extrapolations applied. The RC2 set of standard growth curves available to Michard did not include any curve specific to galaxies more centrally concentrated than n=0.25 objects, and so Michard necessarily applied the growth curve specific to the n=0.25 case to his most centrally concentrated objects. Consistency checks on our extrapolation terms for all of the objects listed in Tableá 3, including the most centrally concentrated ones, can be provided by comparisons with Caon et al.'s total magnitudes. It was found that for objects of (with a scatter of 0.24á mag. about the mean offset):
and (with a scatter of 0.14á mag.):
where `extrapolated' values are from Caon et al. (1990) Tableá I and `integrated' values are from Caon et al. (1990) Tableá VI or Caon et al. (1994). For objects of n < 0.25 on the other hand, it was found that (with a scatter of 0.31á mag.):
and (with a scatter of 0.17á mag.):
In the latter case, if NGCá 4406 were excluded3, we find that (with a scatter of 0.09á mag.):
The agreement with Caon et al.'s integrated magnitudes is therefore very good and much better than with Caon et al.'s extrapolated values. This is reassuring because integrations to large radii should yield relatively unbiased (even if often relatively noisy) estimates of total magnitude4. The disagreements with Caon et al.'s extrapolated magnitudes and Michard's values at the bright end are therefore no cause for concern. Both of the latter sources of magnitude estimates are strongly affected by the
-law extrapolations applied-especially in the cases of the most centrally concentrated objects. As far as our profile fits and parameterisations for the most centrally concentrated objects are concerned, the almost perfect agreement between the Bt(systemic) and Bt(integrated to & extrapolated) values listed in Tableá 35, would appear to confirm the superiority of our fits with respect to ones rigidly assuming n=0.25. Furthermore, our finding that the profiles of the brightest early-type Virgo galaxies are best fitted by Sö©rsic profiles of n<0.25 is in full agreement with Graham et al.'s (1996) conclusion that brightest cluster galaxies typically have n<0.256.
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Title/Abstract Page: Total Magnitudes of Virgo
Previous Section: Bright galaxy sample (14th-8th
á© Copyright Astronomical Society of Australia 1997