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Notes for object NGC 3998

22 note(s) found in NED.

1. 2009ApJ...703.1034Y
Re:NGC 3998
NGC 3998. We find that it is hard to model the X-ray emission using an ADAF with
outflow because the predicted spectrum of an ADAF is too hard. This conclusion
is the same as in Ptak et al. (2004). If we abandon the requirement of
significant outflow and direct electron heating (i.e., {delta} << 1), we can fit
the X-ray spectrum well, as in Ptak et al. (2004). But this kind of ADAF model
is not favored from a theoretical point of view. On the other hand, a jet alone
can fit the X-ray spectrum well, although we again require p < 2 (1.8).

2. 2008MNRAS.386.2242H
Re:NGC 3998
NGC 3998 - The black hole mass is linearly modified with distance taken
from Tonry et al. (2001), the 1{sigma} error is estimated from fig. 12
of De Francesco, Capetti & Marconi (2006).

3. 2008MNRAS.386.2242H
Re:NGC 3998
NGC 3998 - The black hole mass is linearly modified with distance taken from
Tonry et al. (2001), the 1{sigma} error is estimated from fig. 12 of De
Francesco, Capetti & Marconi (2006).

4. 2007MNRAS.377.1696M
Re:NGC 3998
NGC 3998. In this nucleus, Filho, Barthel & Ho (2002) have measured a variable
radio core that is unresolved at 5-mas resolution with VLBI, with a mean 6-cm
flux of 83 mJy.
In the UV, M05 measured in 2002-2003 a monotonic 20 per cent decline in UV
flux in the F250W and F330W bands (means of 199 * 10^-17^ and 153 * 10^-17^ erg
cm^-2^ s^-1^ A^-1^, respectively), over the 11 months they observed it. These
variations provide firm lower limits on the AGN flux. On long time-scales, the
mean 2500-A flux level in 2003 was about five times lower than that reported by
Fabbiano et al. (1994; 10^-14^ erg cm^-2^ s^-1^ A^-1^) at 1740 A in 1992, based
on FOC measurements. There is thus evidence for a large variable UV flux, of the
order of 10^-14^ erg cm^-2^ s^-1^ A^-1^. However, because of the different UV
band, I will not adopt the Fabbiano, Fassnacht & Trinchieri (1994) point as a
lower limit, and conservatively use only the variable flux measured by M05. Ptak
et al. (2004) used the optical monitor on XMM-Newton to roughly estimate a
2100-A UV flux of 250-500 * 10^-17^ erg cm^-2^ s^-1^ A^-1^ in 2001, intermediate
to the 1992 and 2003 levels.
The X-ray flux found by Ptak et al. (2004) using XMM-Newton is 1100 *
10^-14^ erg cm^-2^ s^-1^ at 2-10 keV, and is consistent with, though perhaps a
factor of ~2 higher, previous X-ray measurements over the past two decades. The
photon index is {GAMMA} = 1.9.
A central BH mass of 2.7 * 10^8^ M_[IMAGE]_ has been measured by de
Francesco, Capetti & Marconi (2006) using gas kinematics.

5. 2004MNRAS.350.1087S
Re:NGC 3998
NGC 3998: we have fitted to this SA00 galaxy a Freeman type II disc with
r_cut_= 2.75 kpc (30 arcsec).

6. 2002MNRAS.329..877C
Re:GB6 J1157+5527
90-redshift from Falco et al. (1999); spectrum in Ho et al. (1995);
broad H{alpha}(?); classification in NED is Sy1-LINER.

7. 2002ApJS..139....1T
Re:NGC 3998
NGC 3998 (L1.9).-ASCA results are presented in Ptak et al. (1999). An
Fe K line is marginally detected at 6.4 keV. A recent BeppoSAX
observation (Pellegrini et al. 2000a) has shown that the spectrum from
0.1 to 100 keV is well represented by a power law. The Fe K line was
not detected in the BeppoSAX spectrum to an EW upper limit of 40 eV.

8. 2002ApJ...574..740T
Re:NGC 3998
NGC 4594 (Kormendy et al. 1996b), NGC 4486B (Kormendy et al. 1997),
NGC 4350 (Pignatelli, Salucci, & Danese 2001), NGC 3031 = M81, and
NGC 3998 (Bower et al. 2000) exhibit strong evidence from stellar
dynamics for a black hole but do not yet have three-integral dynamical

9. 2002AJ....124..675C
Re:UGC 06946
Radio tails extending north and south?

10. 2000ApJ...530..688A
Re:NGC 3998
NGC 3998.-The optical line ratios (Ho et al. 1993) of NGC 3998 meet
the LINER definition. The detection of broad H{alpha} (see Ho et al.
1997c and references therein) makes NGC 3998 another candidate for
AGN-dominated LINER. This galaxy is in common with Larkin et al. (1998)
study of LINERs. Their measured [Fe II] 1.257 micron/Pa{beta} line ratio
is lower than ours. Comparing our spectrum with theirs, our detection of
the [Fe II] 1.257 micron line has a higher signal to noise. Larkin et
al. (1998) claimed that the [Fe II] 1.257 micron/Pa{beta} ratio was
significantly lower in comparison with the [O I] {lambda}6300/H{alpha}
ratio. However, with our [Fe II] 1.257 micron/Pa{beta} line ratio
measured from the stellar continuum subtracted spectrum, the galaxy fits
perfectly in the correlation (see Fig. 6). NGC 3998 is another example
of AGN-dominated LINER.

11. 1998ApJS..114...59L
Re:NGC 3998
NGC 3998.--This is a true LINER that shows increasing ratios of [O I] and
[O II] to [O III] with increasing aperture size. The only detected infrared
emission line is [Fe II], which is detected at the 4-5{sigma} level. Using the
estimated Pa{beta} flux, the ratio of [Fe II] to Pa{beta} is 0.6, which is one
of the lowest in the sample. H_2_ is undetected, which sets a low limit for the
H_2_/Br{gamma} ratio. Both of these ratios are significantly lower in
comparison to the O I/H{alpha} ratio than the other LINERs in the sample. The
limit of the ratio of H_2_ to [Fe II], however, does lie along the main
correlation for LINERs and other galaxies. In Larkin et al. (1998), it is
argued that the N II emission is significantly extended in comparison to the
H{alpha}. It is probable that the O I, and also probably the [Fe II] and H_2_,
are also more extended than the H recombination lines and that the optical
ratio calculated in the larger aperture is enhanced in comparison to the
infrared ratios in a much smaller aperture. If true, then the infrared ratios
in a larger aperture would probably be greater and NGC 3998 would lie closer to
the main correlations shown in Figures 2 and 3. In principle, this says that
the low-ionization lines are more extended than H{alpha} and that the
unresolved core has more Seyfert-like line ratios. The Na and Mg absorption
features may be present at a very low level. Optical spectra show prominent
broad H{alpha} wings and even a broadened [O I] line (700 km s^-1^). Optical
absorption features, if present, are weak and broadened (Filippenko & Sargent
1985). Like NGC 404, NGC 3998 has had a strong UV point source detected by HST
(Fabbiano, Fassnacht, & Trinchieri 1994). Coupled with the broad H, this makes
NGC 3998 a prime candidate for a low-luminosity Seyfert galaxy.

12. 1997ApJS..112..391H
Re:NGC 3998
NGC 3998.--Broad H{alpha} is unmistakably present in this famous LINER (Fig.
11a). as was already known from several previous studies (Heckman 1980;
Blackman, Wilson, & Ward 1983; Keel 1983; Paper I). Reichert et al. (1992)
found that Mg II {lambda}2800 also has a broad component, similar in width to
broad H{alpha}. The narrow-line profile, as judged from the [S II] doublet, is
quite systematic and can be represented by the sum of a narrow and a broader
Gaussian. The flux of broad H{alpha}, as determined from our three standard
fitting methods, showed excellent agreement (differing by less than 5% from
each other), and we obtained the final value by averaging all three results.
The adopted broad H{alpha} component contains ~37% of the flux of the entire
H{alpha}+[N II] blend and has widths of FWHM~2150 km s^-1^ and FWZI>~5000 km
s^-1^. Broad H{beta} is also present.

13. 1997AJ....113..950F
Re:NGC 3998
NGC 3998. NGC 3998 is classified as a low-ionization emission-line region
(LINER) galaxy (Heckman 1980) and clearly displays exceptional nuclear
activity (see Fig. 7). The nucleus of NGC 3998 contains a compact
flat-spectrum radio source (Hummel 1980) and is also an X-ray source (Dressel
& Wilson 1985). Ford et al. (1986) showed a narrow-band H{alpha} image in
which a 90" long S-shaped structure is seen positioned intermediate between
the major- and minor-axis.

14. 1997A&A...319...33A
Re:NGC 3998
NGC 3998 Not shown in a figure here, this field is complicated because there is
a galaxy cluster (A1436) in the NE corner (~50'). Near it is a source C=115.6
which coincides with a bright red star (E=9.83, O-E=1.98). More central to the
field, the source C=46.2 coincides with another red star (E=8.67 mag.;
O-E=3.14). About 24' SE of NGC 3998 is NGC 3982, a B_T_^0,i^=11.59 mag., Sey 2
at cz_0_=1195 km s^-1^. NGC 3998 at B_T_^i,0^ = 11.50, cz_0_=1214 km s^-1^ is in
the nature of a more active companion to NGC 3982. The latter is close to a
weak X-ray source and there is a line of weak X-ray sources approximately
across it. Stronger X-ray sources pair across the stronger X-ray Seyfert
NGC 3998 at C=8.9 and 11.9 and, in a slightly different direction, C=8.7 and
6.7. Because of the confused nature of this field identification of these
sources has not been attempted.

15. 1996ApJ...459..110F
Re:NGC 3998
NGC 3998
The nuclear regions of NGC 3998 have been classified as a low-ionization
emission-line region (LINER) (Giuricin et al. 1991). Strong H{beta}, [O III]
4959 A, [O III] 5007 A, and [N II] 5200 A emission are apparent in our
major-axis spectrum. Because of the strong emission, the line strengths in the
central regions could not be reliably determined.

16. 1995ApJS...98..477H
Re:NGC 3998
This well-studied LINER has a weak, broad component of H{alpha} emission
(Paper I) similar to that of M81. Reichert et al (1992) investigated the
ultraviolet (UV) properties of NGC 3998 using spectra obtained with the
International Ultraviolet Explorer}. Although they find that the
spectrum of the central region in the UV is still dominated by
starlight, there may be an underlying power law continuum whose UV flux
is sufficient to produce the observed emission-line spectrum by
photoionization. Reichert et al detected a broad component in the Mg II
{lambda}2800 emission line with a width similar to that seen in the
H{alpha} line. Recent X-ray observations using ROSAT reveal that the
0.2-2.4 keV flux is concentrated in a point source; however, the limited
spectral data are consistent with a variety of models, and thus do not
provide very useful constraints on the possible emission mechanisms
(Reichert, Mushotzky, & Filippenko 1994).

17. 1994CAG1..B...0000S
Re:NGC 3998
April 28/29, 1979
12 min
NGC 3998 has pronounced S0 characteristics,
making it a prototype example of its
class. The extended outer envelope with its
apparent sharp break at the edge of the central
bulge is well shown in the print here. The distance
modulus of m - M = 31.9, based on a redshift of
v_o = 1214 km/s, makes possible the identification
of the condensations over the image as
globular clusters.

18. 1994CAG1..B...0000S
Re:NGC 3998
April 28/29, 1979
12 min
Prototypical S0_1_.

19. 1994A&AS..105..481M
Re:NGC 3998
NGC 3998: The light profile, with a faint ring and a lens, suggests a
disk dominated S0.

20. 1976RC2...C...0000d
Re:NGC 3998
= Holm 310a
Non-interacting pair with NGC 3990 at 3.2 arcmin
Ap. J., 142, 634, 1965.
Ap. J. (Letters), 160, L79, 1970.
Ap. J. (Letters), 164, L35, 1971.
Observatory, 88, 239, 1968.
Ap. J. (Letters), 193, L49, 1974.
Rotation Curve and Systemic Velocity
Ap. J. (Letters), 160, L79, 1970.
Astr. Ap., 8, 364, 1970.
Radio Observations:
Ap. J., 157, 481, 1969.
A.J., 75, 523, 1970.
IAU Symp. No.44, 222, 1972.

21. 1973UGC...C...0000N
Re:UGC 06946
SA(r)0/a? (de Vaucouleurs)
See UGC 06938
Companion 4.7, 145, 0.3: x 0.3:, diffuse

22. 1964RC1...C...0000d
Re:NGC 3998
= Holm 310a
Very bright nucleus: 0.5 arcmin x 0.4 arcmin. Bright uniform lens:
1.4 arcmin x 1.2 arcmin.
See also HA, 105, 230, 1937.
Non-interacting pair with NGC 3990 at 3.2 arcmin.
Ap. J., 85, 325, 1937.
I.A.U. Symp., No. 5, 1958 = Lick Contr. II, No. 81, 1958.

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